Abstract:
This disclosure describes single-use test cartridges, cell analyzer apparatus, and methods for automatically performing microscopic cell analysis tasks, such as counting blood cells in biological samples. A small unmeasured quantity of a biological sample such as whole blood is placed in the disposable test cartridge which is then inserted into the cell analyzer. The analyzer isolates a precise volume of the biological sample, mixes it with self-contained reagents and transfers the entire volume to an imaging chamber. The geometry of the imaging chamber is chosen to maintain the uniformity of the mixture, and to prevent cells from crowding or clumping, when it is transferred into the imaging chamber. Images of essentially all of the cellular components within the imaging chamber are analyzed to obtain counts per unit volume. The devices, apparatus and methods described may be used to analyze a small quantity of whole blood to obtain counts per unit volume of red blood cells, white blood cells, including sub-groups of white cells, platelets and measurements related to these bodies.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 15/017,498, filed Feb. 5, 2016, which is a continuation in part of U.S. application Ser. No. 14/947,971, filed Nov. 20, 2015, which claims priority to U.S. provisional application Nos. 62/138,359, filed Mar. 25, 2015, 62/113,360 filed Feb. 6, 2015, and 62/084,760, filed Nov. 26, 2014, which are all herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention pertains to analyzers and methods for automatically performing microscopic cell analysis tasks, such as counting blood cells in biological samples. More specifically, the present disclosure relates to single use devices, apparatus and methods used to count red blood cells, white blood cells and platelets, and measurements related to these bodies. 
     BACKGROUND OF THE INVENTION 
     There are a variety of methods for enumerating particles, such as cells in a biological sample. Determining the number of cells per unit volume in a sample provides the physician important diagnostic information. The most elementary method of counting cells consists of introducing a diluted biological sample into a hemocytometer and examining it with a microscope. A hemocytometer is a device with an optically clear chamber having a known depth, typically 100 microns, and ruled markings to define a unit volume, typically 0.01 μL. A uniform mixture of diluted whole blood, for example, may be introduced into the hemocytometer by capillary action to form a monolayer. Using a microscope to visualize the diluted sample, cells of different types can be counted manually in a limited number of marked areas. Counts are aggregated to compute the number of cells per unit volume. This manual method is time consuming, tedious, and requires a skilled technician to operate the microscope and to recognize the various types of cells, and is prone to error. Its accuracy is limited by the number of cells counted and the homogeneity of the monolayer formed by introduction of the diluted sample. 
     Consequently, automated methods, such as impedancemetry (Coulter principle U.S. Pat. No. 2,656,508) and flow cytometry, have been developed for rapid counting, sizing, and classification of a relatively large number of cells for diagnostic tests such as the Complete Blood Count (CBC) or CBC with a five part differential. These automated methods also have shortcomings. The analyzers are relatively large and expensive and require skilled operators for their use and maintenance. Such analyzers are typically available only in centralized laboratories. Blood samples are collected in special containers having an anticoagulant to keep the blood from clotting while being transported to the lab. This process adds costs and risk of erroneous results from transport, handling, labeling and transcription, as well as a time delay in obtaining the results. 
     The CBC generally includes measures of white blood cells (leukocytes) per unit volume (WBC), red blood cells (erythrocytes) per unit volume (RBC), platelets (thrombocytes) per unit volume (PLT), hematocrit (HCT) or packed cell volume (PCV), hemoglobin (HGB), and measurements related to red cells including mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin content (MCHC), and red cell distribution width (RDW). A diagnostic test referred to as a “CBC with differential”, also known as a “CBC with five part diff”, will also include Neutrophil granulocytes (NEU), Lymphocytes (LYM), Monocytes (MON), Eosinophil granulocytes (EO) and Basophil granulocytes (BASO) per unit volume or as a percentage of the white blood cells (WBC). The CBC with differential also may include counts of Immature Cells (IC), nucleated Red Blood Cells (nRBC), and Reticulocytes (RETIC) per unit volume of the blood sample. 
     The CBC provides a panel of blood cell measurements that can be used to diagnose a wide variety of abnormal conditions, such as anemia or infection, or to monitor a patient&#39;s treatment, such as chemotherapy. Because of its usefulness, the CBC analysis is one of the most commonly performed diagnostic tests in medicine, but patients typically wait a day or more for results. If microscopic cell analysis could be performed in a portable, easy-to-use, analyzer close to the patient, results could have a more immediate impact in improving patient care. A simple system able to provide the CBC in the physician&#39;s office, or at bedside, or in the Critical Care Unit (CCU) or Intensive Care Unit (ICU), within a few minutes and using a drop of blood from a finger-stick, could have enormous impact on the delivery and affordability of health care. 
     Recent patent documents have described simpler devices than centralized lab hematology analyzers for performing cell analysis of blood samples. In U.S. Pat. No. 7,771,658, issued to Larsen, the applicant, provides technology for performing a flow-cell analysis of blood cells in a single use disposable cartridge. Larsen describes means for taking an exact amount of blood sample, diluting the amount of blood with a precise volume of diluent, and mixing the blood with the diluent to obtain a homogeneous solution. Larsen utilizes a single use cartridge to flow a measured amount of the mixture of sample and diluent through an orifice at a rate of several thousand particles per second, and counts, sizes, and classifies the particles for analysis in accordance with the Coulter principle. Because Larsen&#39;s disclosure is directed to the analysis of a small sample of whole blood, errors in metering various volumes or in the mixing or sampling steps can significantly impact the accuracy of the results. 
     PCT Patent Number WO 2014099629 issued to Ozcan et al. describes a system for analyzing a blood sample with a mobile electronic device having a camera. The sample preparation process for each test requires accurate measurement of 10 μL of whole blood to be mixed with 85 μL phosphate buffered saline and 5 μL of nucleic acid stain. Ten (10) μL of this diluted mixed sample are then loaded into a cell counting chamber with precise channel height of 100 μm and are imaged by a digital camera. A separate cell counting chamber is needed for analysis of red cells, white cells, and hemoglobin, and each test should be performed separately. Accuracy of the final result is not only dependent on the accurate measurements of the various sample preparation steps, including the precise metering of the sample and diluent, but also on the precise fabrication of the counting chambers. Maintaining uniformity and consistency of the 100 μm dimension of the channel height in a disposable cartridge is difficult to achieve in a low cost device. 
     U.S. Pat. No. 8,837,803 to Wang et al. describes a method for determining cell volume of red blood cells, which seeks to avoid the errors associated with diluting, mixing, and sampling, by analyzing a sample of substantially undiluted whole blood. In theory this approach has appeal, but the handling of undiluted whole blood is challenging. The cells are so numerous (for example 5,000,000 red cells in 1 μL) that their distribution can be impacted by contact with the surfaces of a disposable cartridge. Additionally, in order to image cells in this overcrowded environment, the imaging chamber should have a depth of only a few microns to prevent the overlapping of cells, and it should be fabricated accurately, because it determines the volume of the blood sample being analyzed. 
     Therefore a compact, accurate method of performing microscopic cell analysis using digital camera imaging of a diluted sample, which does not require accurate measurement of the diluent volume, or require accurate or precise dimensions of an imaging chamber, is highly desirable. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide an apparatus that can provide counts of cells or other particles of a biological sample per unit volume without requiring an operator having specialized knowledge or specialized skills. Another objective of the present invention is to provide an easy-to-use apparatus that can perform all of the measurements of the CBC in a few minutes. Another objective of the present invention is to provide a method for determining the concentration of particles in a diluted biological sample that does not require accurate measurement of a volume of diluent or reagent mixed with the sample. Another objective of the present invention is to provide ready-to-use reagents for use in performing the microscopic analysis of a biological sample that do not require preparation, mixing or measurement by the user. Another object of the invention is to create a substantially homogenous monolayer of cells of a diluted sample in a single use disposable device and to perform a CBC analysis in a few minutes. Another objective is to provide a sample collection device that can easily be operated by a user to obtain a biological sample for analysis. Yet another objective is to provide all of the fluidic components of an apparatus to perform a CBC in a single-use device, so as to prevent cross contamination between samples and to avoid the need for cleaning and washing of fluidic components. Another objective of the present invention is to provide internal monitoring of the critical process steps of counting cells, so that a potentially erroneous result can be flagged. Still another objective is to provide a method of performing the CBC immediately after collecting the sample, and to eliminate transport of the sample to a laboratory or storage of the sample. Some or all of these and/or other objectives or advantages may be accomplished by embodiments of the invention as provided for in the appended claims. 
     The disclosure provides improved methods, systems, and devices for performing counts and measurements of particles in a biological sample. Aspects of the disclosure are directed to determining the concentration of one or more types of particles and providing the result as the number of such particles per unit volume of the biological sample in a few minutes. The particles may be any mass suspended in a liquid that can be recognized by optical inspection using an automated microscope and image analysis techniques well known in the art. Examples of particles include, but are not limited to, blood cells, sperm, bacteria, spores, and inorganic particles. 
     While embodiments of the present invention can be used in many applications to count particles suspended in a liquid, the present disclosure will demonstrate benefits of the invention in performing the Complete Blood Count (CBC) or CBC with differential on human blood samples as defined above. The present disclosure describes a single-use test cartridge for use with an apparatus that includes an automated microscope for analyzing cells in a biological sample. The test cartridge is used to collect a biological sample. For example the user can prick the finger of a patient and obtain a whole blood sample and collect the resulting drop of blood in the test cartridge. The user can accomplish this by holding the test cartridge beneath the hanging drop from the patient&#39;s finger and then bringing it closer until the drop contacts an input port or sample cup on the test cartridge. In an alternate embodiment, the user may collect a blood sample intravenously and transfer it to the test cartridge using a capillary tube or plastic bulb pipette. In one example the single-use test cartridge includes an input port adapted to accept a variety of sources of biological samples including a direct sample, capillary tube, or transfer pipette. In another example, the test cartridge could draw a sample into it by capillary action. The test cartridge may also include a closure that the user applies to cover the input port after the sample has been collected into the test cartridge. The closure may be part of the test cartridge or a separate device. The user may apply the closure manually or the apparatus may automatically move the closure to cover the input port when the test cartridge is docked to the apparatus. The closure provides a physical barrier to avoid subsequent contact with any excess sample on the surface of the test cartridge. The closure has a vent to provide an air path to the input port to allow the liquid sample to move within the test cartridge, as will be described below. 
     Within the test cartridge, the input port is connected by an input channel to a metering chamber capable of precisely separating a small volume of the sample from the unmeasured sample. As an example, the collected sample volume may be 5-20 μL, of which the metering chamber separates out or isolates 0.1-5 μL for measurement. If a finger stick sample is utilized, a sample volume less than 10 μL will minimize the risk of hemolysis and the risk of dilution by interstitial fluids. The metering chamber can be a section of a fluid channel, a cavity, or a pass-through conduit within a valve, or another volumetric shape that can be reproducibly fabricated to contain a predetermined volume of the biological sample in the range of 0.1 to 5 μL. Injection molding, compression molding, etching or other processes known to those skilled in the making of lab-on-a-chip or microfluidic devices can be utilized to manufacture the metering chamber. 
     In one example, the metering chamber is combined with a rotary valve structure by molding a pass-through conduit in the cylindrical stem of the rotary valve. As an example a pass-through conduit having a cylindrical cross section with 0.5 mm diameter and a length of 5 mm, has an internal volume of approximately 1 μL. The pass-through conduit is initially filled with the biological sample by providing a fluid communication path between the input port and input channel, the pass-through conduit, and a vacuum channel. A vacuum applied to the vacuum channel pulls the sample into the pass-through conduit. Alternatively the biological sample can be pulled into the pass-through conduit by capillary attraction. Once the biological sample has completely filled the pass-through conduit, the cylindrical stem of the rotary valve is rotated until the pass-through conduit is no longer connected to the input channel or the vacuum channel, thus separating or isolating the sample volume contained in the pass-through conduit. Alternatively, a rotary face seal valve, a slide valve or a fixed geometry in the test cartridge could be used to isolate a small volume of the sample. 
     Further, elements of the test cartridge include a prepackaged liquid reagent or alternatively, a chamber for storing a liquid reagent, together with a mixing chamber, an imaging chamber, and fluid channels through which the sample and liquid reagent may be moved. In one example, after the biological sample has filled the pass-through conduit, the rotary valve is positioned so that the pass-through conduit is placed in fluid communication with both a liquid reagent and the mixing chamber. Empirical studies have determined that a volume of diluent or liquid reagent or stain (referred to here as “diluent/reagent”) that is in excess of 3-times the volume of the pass-through conduit is sufficient to wash out the entire isolated sample. In one example, the diluent/reagent is a combination of diluent and stain and is supplied in a volume to provide a dilution ratio of about 40:1. Therefore forty times the volume of the metering chamber can be used to push the isolated sample out of the pass-through conduit and into the mixing chamber, where the sample is uniformly mixed with the diluent/reagent, and then transferred into the imaging chamber. 
     The single use test cartridge contains an imaging chamber, through which an automated microscope can acquire images of cells in the mixture of diluent/reagent and sample. In one embodiment of the present invention, the isolated sample is diluted with a known volume of diluent/reagent, whereby the dilution ratio is established. The volume of the diluent/reagent may be determined by measuring it, for example, by monitoring its flow in a fluid channel of known dimensions with a camera or other fluid sensor such as optical reflective/transmittive or ultrasonic, or by temporarily metering it into a known volume chamber and then using only that known volume for sample dilution. According to this embodiment, the cells in a known volume of the diluted sample are counted, and because the dilution ratio is known, the cell counts per unit volume of the blood sample can be determined. The volume of the diluted sample can be known by filling an imaging chamber of known volume with the diluted sample. The volume of the imaging chamber may be known by using highly reproducible manufacturing processes, or by measuring each test cartridge at time of manufacture and encoding sizing parameters in the package labeling. Alternatively, a measured amount of the diluted sample can be transferred into an imaging chamber of unknown volume and counting all the cells in the chamber. A measured amount of the diluted sample can be determined by monitoring its flow from the mixing chamber into a fluid channel of known dimensions by a camera, and isolating a segment. The segment, in turn, is moved into the imaging chamber. 
     In a preferred embodiment, the entire isolated sample is transferred to the mixing chamber and then to the imaging chamber. According to this embodiment, neither the dilution ratio nor the volume of the diluent needs to be known. The size of the imaging chamber is chosen to ensure that the entire volume of the isolated sample and the diluent/reagent can be contained within the imaging chamber, but the exact dimensions or volume of the chamber do not need to be known. The depth of the imaging chamber should be small enough to prevent the cells from overlapping at the chosen dilution ratio when the cells settle to the bottom. This depth is preferably between about 10 μm and 200 μm. In one embodiment, the depth of the imaging chamber is 100 μm and the ratio of the diluent/reagent to the isolated sample is 40 to 1. The width of the imaging chamber is chosen to provide uniform filling by the different cell sizes and smooth flow without forming voids or crowding of cells. The length of the imaging chamber is calculated based on the depth and width parameters to provide the volume needed to accommodate the entire isolated sample at the chosen dilution ratio, and to provide a margin of safety. The shape of the imaging chamber may further be chosen to match the field of view of the digital camera or to facilitate capture of multiple images or to maintain a uniform distribution of cells 
     We have found that if the shape of the imaging chamber is square or rectangular having a ratio of length to width of 2:1, the cells will not uniformly fill the imaging chamber. If the mixture of sample and diluent/reagent is uniform when it enters the imaging chamber, the cells will tend to bunch and crowd, particularly near the sides or edges, and when they settle, the layer on the bottom of the imaging chamber will not be homogenous. It is important to obtain a substantially homogenous monolayer of cells in the imaging chamber, as this facilitates the counting of all the cells. We have found that if the width and depth of the imaging chamber are small compared to the length, the cells remain more uniformly distributed. Desirably, the length-to-width ratio of the imaging chamber is greater than 10:1. In various embodiments of the present invention, the shape of an imaging chamber may be serpentine, helical, or castellated according to the form factor of the test cartridge. In all of these cases the width and depth are small compared to the length so that the cells due not aggregate on the sides or corners of the imaging chamber, and the layer of cells settling to the bottom of the imaging chamber is substantially homogenous. Those skilled in the art will recognize that other geometries for the imaging chamber, which maintain the distribution of cells when the mixed solution of sample and diluent/reagent is transferred into the imaging chamber may also be utilized. 
     The design goal of any imaging chamber is to contain all the cells from the original metered chamber and the diluent/reagent in a uniform manner and without significant cell overlap when the cells settle to the bottom of the imaging chamber. The dilution ratio combined with the depth of the imaging chamber can be chosen to minimize the overlapping. As an illustrative example, an imaging chamber may have a width between 0.5 mm and 2.5 mm, a depth from 10 to 200 μm, and the dilution ratio may be from 10:1 to 100:1. 
     Materials, which contact the cells outside of the imaging chamber, may be chosen to have surface properties to minimize cell adherence. Liquid reagents, which may include a surfactant or cell sphering agent to facilitate cell analysis, may also advantageously minimize red cells being lost during transfer or being overlapped in the imaging chamber. The volume of liquid reagent and the flow velocity may also be chosen to improve the likelihood of transferring every cell from the metering or mixing chamber to the imaging chamber and insuring that the distribution of the cells remains uniform. Yeh-Chan Ahn describes the complex convective diffusion phenomena that is created in a serpentine microchannel which has a varying curvature (See  Investigation of laminar dispersion with optical coherence tomography and optical Doppler tomography , Yeh-Chan Ahn, Woonggyu Jung, Jun Zhang, and Zhongping Chen, OPTICS EXPRESS 8164, Vol. 13, No. 20, 3 Oct. 2005). Particles, or in our case, cells which are in suspension and moving through such a microchannel tend to segregate according to their size, density, channel shape and flow velocity. Secondary flow from the serpentine geometry can create vortices as the channel curves causing the cells to be re-mixed into the center of the flow at certain fill velocities. This re-mixing helps maintain a near uniform distribution of the cells as the fluid fills the microchannel. In one embodiment, we have found that a serpentine path that is 1.25 mm wide with turning inside diameter of 1.25 mm and an outside diameter of 2.5 mm, a depth of 0.125 mm, a length of 500 mm, and an effective fill speed of about 2 μL/s insures that the flow of cells remains uniform. 
     It should be noted that the time to count every cell is directly related to the volume of the metered chamber, and that this creates a trade-off in overall performance. Manufacturing highly reproducible metering chambers is challenging for very small volumes. Therefore while it may be easier and more reproducible to manufacture a metering chamber with a 5 μL volume than one with a 1 μL volume, the 5 uL volume of sample would potentially take five times longer to analyze. Embodiments of the present invention can provide a solution to this dilemma. By ensuring that the sample and diluent/reagent are well mixed and that a proper dilution ratio is chosen, and by utilizing a serpentine shaped imaging chamber where the length is large compared to the width and depth, the pattern of cells across the imaging chamber is relatively uniform and highly reproducible. Under these conditions, the layer of cells settling to the bottom of the imaging chamber will be a substantially homogenous monolayer. As a result, instead of imaging the entire layer and counting every cell, one can take representative images or frames that are statistically derived to accurately account for every cell. Thus, within the allowable error for the final result(s), every cell is included in the analysis, whether by actual image or by statistical representation. As an illustrative example, the camera may take up to 20,000 images at 20× in order to scan the entire imaging chamber. Alternatively, every tenth frame could be taken to obtain a statistical representation. Another option would be to divide the imaging chamber into segments and count the cells in every other segment or every third segment and so on. Another alternative to decrease the imaging time would be to scan the entire imaging chamber at 10×/0.25 NA or 4×/0.1 NA to obtain the total WBC and RBC total counts, and then take images at higher power (20×.4 NA or higher) to obtain the higher-resolution detail needed for counting platelets, reticulocytes, and performing the WBC differential. 
     Embodiments of the present invention can achieve accurate results that are not dependent on many factors that have impacted the accuracy of results in the prior art. For example, the volume of the diluent/reagent and the dilution ratio do not impact the results, so long as all the cells from the metered volume are transferred to the imaging chamber and presented for analysis. Similarly the representativeness of a selected sub-volume of the mixture of sample and reagent, and the homogeneity of the sub-volume, which directly affect the accuracy of results by prior art methods, need have no impact on embodiments the present invention. Most importantly, the depth and uniformity of the imaging chamber, which has been difficult or expensive to control in other prior art efforts, need not impact the accuracy of results according to embodiments of the present invention. 
     The present disclosure further describes a cell analyzer that is small and easy to use. The cell analyzer accepts the test cartridge and carries out all the steps of the cell analysis without further input from the user. In one embodiment, the test cartridge contains all diluents and reagents needed to perform a CBC analysis of the patient sample placed in it. In this embodiment, the cell analyzer has fluid handling components including positive and negative pressure sources that interface with the test cartridge when it is placed into the analyzer. One or more connections are made between the analyzer and the cartridge to place these pressure sources into fluid communication with channels in the cartridge to provide a motive force to move liquids within the cartridge. The cell analyzer also has a mechanical valve driver for operating a valve in the test cartridge for controlling the movements of fluids in the test cartridge. When the test cartridge is placed in the analyzer, the mechanical valve driver is connected to a valve indexer to provide means for operating the valve in the test cartridge. The cell analyzer includes a mechanism for release of the diluent/reagent that are stored on board the test cartridge. The cell analyzer further includes fluid control logic to automatically control movement of the fluids in the test cartridge by activating the positive and negative pressure or displacement sources and operating the mechanical valve driver according to pre-programmed sequences. The cell analyzer may include a process monitoring camera positioned to acquire digital images of the movement of fluids in the cartridge. Information from the process monitoring camera can be used to provide feedback for the fluid control logic or for monitoring critical steps. 
     The present disclosure also provides devices and methods for managing and/or monitoring the sample collection and preparation process to ensure accurate results. In applications where the present invention is used to perform a CBC analysis, if too much time lapses between obtaining the blood sample and completing sample dilution and staining within the test cartridge, the blood may clot or the cells may settle resulting in erroneous results. In one embodiment of the present invention that mitigates this risk, the test cartridge is placed on the analyzer in a slide-out tray which initiates process monitoring within the analyzer. The blood sample is added to the cartridge by dispensing a free-hanging drop, or by using a capillary tube that is inserted into the test cartridge. Immediately after the sample has been added to the cartridge, the user presses “Run Sample” to initiate the test sequence. Because the cartridge is controlled by the analyzer, the time to collect the sample is known and can be short enough to avoid the need for anticoagulant coating or mixing the blood sample. 
     In an alternate embodiment that allows the sample to be collected several minutes before processing, an anticoagulant, such as K2 or K3 EDTA, is provided. This may be achieved by coating the sample input cup with anticoagulant, by use of a capillary tube coated with anticoagulant for a finger-stick sample, or by sampling from an evacuated blood collection tube such as a Becton Dickenson Vacutainer® containing anticoagulant. To manage cell settling, the test cartridge according to this embodiment has a timing indicator which is initiated when the input port is opened or the blood sample is introduced. The timing indicator can be a color-changing chemical reaction, a time delayed thermal reaction, an analog or digital timer, or other means known in the art. When the user loads the test cartridge into the analyzer, the timing indicator is read and if needed, the sample is mixed before proceeding. If too much time has lapsed the sample can be rejected to avoid producing erroneous results. 
     In yet another embodiment that facilitates remote sample collection, the test cartridge is docked to a carrier system. The carrier system is a handheld or portable device used to facilitate a portion, or all, of the sample preparation steps. After blood is added to the test cartridge using any of the above mentioned methods, the carrier system according to this embodiment draws the blood into the cartridge, meters the sample, performs quality checks, and completes the sample preparation to present the cells for image analysis. The carrier system would then either eject the test cartridge for the user to transfer to the imaging analyzer, or the carrier system could be docked to the imaging analyzer for an automated handoff. In this embodiment anticoagulant coatings are not needed and there is no risk of cell settling because the critical steps are initiated as soon as the sample is placed in the test cartridge. 
     Combinations of the workflow devices and methods are also contemplated in the present disclosure. By way of example, a simple carrier system could incorporate a digital timer and a mechanism able to meter the sample, but not perform quality checks or full sample preparation. These additional steps would be done by the cell analyzer. 
     The cell analyzer contains an automated microscope including an objective lens, focusing mechanism, bright-field and fluorescent light sources, filters, a dichroic mirror and a digital camera. In some embodiments, the cell analyzer may further include an illumination source and photometric detector for measuring light transmission at one or multiple wavelengths for measuring the concentration of an analyte in the sample. For example, the test cartridge can include a photometric chamber which is in fluid communication with the input port by means of a fluidic channel, and through which the sample can be transferred for photometric analysis, such as a hemoglobin measurement. 
     By way of example, to measure hemoglobin, the cell analyzer may have an illumination source consisting of two light emitting diodes (LEDs) providing excitation at wavelengths of 502 nm and 880 nm. The light path for the LEDs and a photometric detector are approximately 0.030″ diameter. The 502 nm LED may be selected for absorbance measurement because of an isobestic point of oxyhemoglobin (O2Hb) and deoxyhemoglobin (RHb). Also at 502 nm, the slope of the O2Hb and RHb curves are very low, resulting in minimal variation with varying oxygen saturation (sO2) levels. Furthermore, the carboxyhemoglobin (COHb) curve is also close to this isobestic point, resulting in very little effect from COHb. An 880 nm LED can measure the background scatter effects caused by RBCs, WBCs, lipids, etc. This is particularly important when taking measurements on whole blood. This measurement may also be performed on lysed blood, with or without a reagent for converting the hemoglobin to a single form, such as reduced hemoglobin, methemoglobin, azidemethemoglobin or cyanomethemogloin. In the case of a conversion to a single form of hemoglobin, a different peak wavelength for absorption measurement may be used, such as 540 nm or 555 nm. 
     Disclosed and contemplated aspects also include an example of a test cartridge that is not preloaded with reagents, and instead, is coupled to a reagent supply module contained on board the cell analyzer. The user loads the reagent supply module into the cell analyzer where it is utilized for multiple test cartridges. When the reagent supply module is exhausted or expires, the cell analyzer alerts the user and will not perform additional tests until the reagent supply module is exchanged. The reagent supply module includes a cradle for receiving the test cartridge, a vessel for holding a liquid diluent/reagent, a diluent delivery pump in fluid communication with the vessel, and a diluent/reagent output port constructed to interface with the test cartridge when the cartridge is in the cradle. In one example the size of the vessel is of sufficient capacity to provide diluent/reagents to dilute several samples (50-100) with a reagent to sample ratio of 10:1 to about 250:1. The diluent/reagent supply module may include a self-priming mechanism for priming the liquid reagent and eliminating air bubbles. The reagent supply module may further include a chamber for collecting waste diluent/reagent from the priming process. 
     In another embodiment contemplated in the present disclosure, a small measured volume of whole blood may be mixed manually with an unknown amount of diluent/reagent in a sample preparation device. For instance, the known volume of sample and unknown diluent/reagent may be put into a sample tube and gently rocked back and forth a few times. The entire mixed volume is then transferred by using a transfer pipette or similar device to a test cartridge having an imaging chamber. According to embodiments of the present invention, if all of the cells in the imaging chamber are counted (either directly or by statistical sampling), then the concentration of cells per unit volume can be determined, without one needing to know the volume of the diluent/reagent, the dilution ratio, or the volume of the mixed sample in the imaging chamber, or the volume of the imaging chamber occupied by the mixture. 
     Diluent/reagents that are preloaded in the test cartridge, or are provided in a separate sample preparation device, or by a supply module are in a ready-to-use format. For a CBC analysis, the reagents may include a membrane-permeable dye, such as Acridine Orange to differentially stain the DNA and RNA of cells in whole blood. Other stains known to those skilled in the art, such as cyanine dyes, can also be used to stain the blood cells. In an alternative arrangement, the stain may be provided in a dry reagent form together with a diluent that is mixed with the dry reagent as needed. Multiple stains can be included in a combination reagent. In one embodiment, the reagents may include an antibody conjugated to a detectable label that targets specific cells or specific antigens associated with cells. The detectable label may be a dye, a fluorescent dye, quantum dot, colloidal metal such as gold, silver, or platinum or other detectable constructs known in the art. The detectable label can also be used to detect a cell-specific antibody, such as CD3, CD4, CD14, CD16, CD19, CD34, CD45, CD56, or any other of the enumerated Cluster of Differentiation markers. The detectable label can also be used to detect bacterial or parasitic pathogens, platelets, recirculating tumor cells, leukemic cells, stem cells or any combination of these. 
     In other embodiments the liquid reagent may contain a surfactant such as polysorbate or sodium dodecyl sulfate (SDS), an anticoagulant such as EDTA, and/or a sphering agent such a zwitterionic detergent to provide isovolumetric reshaping of the red blood cells to facilitate cell size measurement and computation of the mean corpuscular volume (MCV). 
     Systems according to the invention can exhibit better quantitative accuracy than manual microscope analyses using a manual hemocytomer or similar device, which tend to be limited by variability in sample preparation and limited counting statistics. In embodiments of the present invention, sample preparation is improved by removing critical operator fluid handling steps and by automation of all dilution steps. Because every cell and platelet is counted in the entire metered volume of sample, any error in the sample dilution is irrelevant. 
     Systems according to the invention can also save time that would otherwise be allocated to manual hemocytometer slide preparation, setup time, and microscope focusing, which can limit the number of blood samples that can be analyzed. Automation can greatly increase the rate of image acquisition and analysis, allowing for more cells to be analyzed and counted. This can improve the counting statistics and overall precision of the system. 
     Systems according to the invention can also extend the capabilities of cell counting methods by enabling CBC point-of-care testing, i.e. near patient testing, to permit immediate clinical decisions to be made. Personnel having a relatively low skill level can operate the systems. The analyzers can be engineered to be inexpensively manufactured and easily serviced, allowing them to be more readily deployed at point-of-care sites, such as at the patient&#39;s bedside, in physician&#39;s offices, and at emergency sites. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which: 
         FIG. 1  is a perspective view of an illustrative test cartridge being positioned to collect a drop of blood from a patient&#39;s finger; 
         FIG. 2A  is a perspective view of an illustrative test cartridge with a cover shown in the open position to receive a biological sample; 
         FIG. 2B  is a perspective view of the test cartridge shown in  FIG. 2A  with the cover shown in the closed position ready for analysis; 
         FIG. 3  is a cut-away view of an illustrative cell analyzer showing internal components with a test cartridge being inserted; 
         FIG. 4  is a plan view of an illustrative test cartridge of the type that includes reagents for conducting a test; 
         FIG. 5  is a plan view of an illustrative test cartridge of the type that does not include reagents; 
         FIG. 6  is a perspective view of an illustrative reagent supply module showing a test cartridge ready to be joined with the module; 
         FIG. 7A  is a perspective bottom view of a metering chamber formed in the face of a valve stem of a rotary valve; 
         FIG. 7B  is a side view of a valve stem with a metering chamber formed as a pass-through conduit; 
         FIG. 8A  is a plan view of an illustrative test cartridge showing a sample of whole blood deposited in the input port area; 
         FIG. 8B  is a plan view of the test cartridge of  FIG. 8A  showing initial movement of the sample and reagent with the rotary valve in the first open position; 
         FIG. 8C  is a plan view of the test cartridge of  FIG. 8B  with the valve in the second open position; 
         FIG. 8D  is a plan view of the test cartridge of  FIG. 8C  illustrating the sample and the reagent in the imaging chamber; 
         FIG. 8E  is a plan view of the test cartridge of  FIG. 8D  illustrating the sample and most of the reagent positioned in the mixing chamber; 
         FIG. 8F  is a plan view of the test cartridge of  FIG. 8E  illustrating all of the sample and the reagent positioned in the imaging chamber and the valve in a final, closed position; 
         FIG. 9  is an side elevation view of a cross section of the passive mixing chamber taken through line  9 - 9 ′ of  FIG. 8E ; 
         FIG. 10  is a plan view of a test cartridge of an alternate test cartridge embodiment. 
         FIG. 11  is a flowchart illustrating the operation of the cell analyzer. 
         FIGS. 12A and 12B  show both bright-field and fluorescent images of the same cells that were collected according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates test cartridge  100  being positioned to collect a drop of blood  120  from a patient&#39;s finger. The test cartridge is held beneath the hanging drop  120 , so that it contacts the input port  130  of the test cartridge  100 . The input port  130  comprises a recessed area or opening that may be coated with an anticoagulant and have surface treatment or features such as small columns to increase surface retention to collect and hold the blood sample. In an alternate embodiment, the blood sample  120  may be collected intravenously and introduced to input port  130  by a transfer pipette or capillary tube. The transfer pipette or capillary may contain an anticoagulant coating according to the desired workflow. The volume of blood or other biological sample placed in input port  130  is sufficient to visually fill the recessed sample area, but is unmeasured. 
       FIG. 2A  shows test cartridge  100  with closure  135  shown in the open position to provide access to input port  130 . Closure  135  is adapted to slide relative to the test cartridge  100  and may have detent or other positioning features that facilitate placing it in different positions. After the biological sample has been collected into input port  130 , closure  135  may be moved to the position shown in  FIG. 2B  to cover the input port  130 . The closure  135  may be moved by the user prior to inserting it into the analyzer as shown in  FIG. 3 . Alternatively, closure  135  may be moved by an operation within the cell analyzer. Alternate embodiments of closure  135  may include graphics, identifying information, or instructions to the user. While the closure  135  is illustrated as a sliding component, other means of closing the input port  130  are contemplated including a cap that hinges upward, a small surface cover that swivels away from and returns to cover the input port  130 , or an adhesive component that sticks to the input port  130  or area surrounding it. In all cases the closure  135  includes a vent or air path to the input port to allow the blood sample to move into the test cartridge  100 . 
       FIG. 3  is a cut-away view of an illustrative cell analyzer  200  with test cartridge  100  positioned so that the operator can introduce it into the analyzer. From the outside of the cell analyzer  200 , one can see the housing  206 , a user-interface screen  208 , a printer  212 , and a cartridge loading door  217 . When the cartridge loading door  217  is opened, the test cartridge  100  can be placed on a cradle  220  of x-y stage  225 , configured to receive test cartridge  100  from the user. The cradle  220  provides mechanical alignment of the cartridge to facilitate connections that are made between the analyzer and the cartridge. For example, a mechanical presser foot  230  may be placed in contact with a flexible surface on the test cartridge to provide mechanical pressure onto packaged, on-board reagents. Some embodiments of the cell analyzer  200  may utilize a reagent supply module  470  as further described with reference to  FIG. 6 . Reagent supply module  470  may be installed on x-y stage  225  and has a receiving area  473  (see  FIG. 6 ) to provide alignment of the test cartridge  402  with the reagent module  470 . 
     A valve driver  235  can be positioned to operate a rotary valve on the test cartridge. A vacuum/pressure pump  240  supplies negative or positive pressure to a manifold  245 , which interfaces with the test cartridge  100  when it is placed in the cell analyzer as described below. The cell analyzer  200  further includes system controller  250  to control movement of the fluids in the test cartridge by activating the vacuum/pressure pump  240 , moving the mechanical presser foot  230 , or operating the valve driver  235  according to pre-programmed sequences. Monitoring camera  255 , positioned to acquire digital images of the fluids in the cartridge, provides feedback for the system controller  250 . Monitoring light source  256  may be a ring illuminator that surrounds the lens of the monitoring camera  255 . Information from the monitoring camera  255  is used to provide feedback for controlling movement of liquids, for positioning the rotary valve, and for confirming critical steps. 
     Also shown in  FIG. 3  are the components that comprise the automated microscope of the cell analyzer  200 . At the base of the analyzer, bright-field light source  260  provides illumination through the test cartridge to the objective lens  265 , operatively coupled to focusing mechanism  267 . At the top of the analyzer, fluorescent light source  270  provides illumination through dichroic mirror  277  to provide fluorescent excitation of the sample. At the rear of the analyzer, digital camera  280  captures images of the test cartridge  100  and transmits them to image processor/computer  290 . In some embodiments, the cell analyzer may further include a photometric light source  293  and photometric detector  295  for measuring light transmission at one or multiple wavelengths in a chamber in test cartridge  100 , such as for measuring hemoglobin, as is more fully explained below. 
       FIG. 4  shows an illustrative test cartridge  401  of the type that includes liquid reagents stored in a blister pack  417  for conducting a test. The test cartridge  401  has an input port  407  for receiving a sample, a passive mixing chamber  405  for mixing the sample with diluent/reagent, and an imaging chamber  403  for capturing images of the cells in the mixture of sample and diluent/reagent for analysis. In this embodiment, photometric chamber  409  may be filled with whole blood to make optical absorbance measurements to determine concentrations of certain analytes in the sample, such as hemoglobin. A rotary valve  415  provides fluidic connections between various fluidic channels, vents, and ports, including sample driver port  411 , vent  423  and mixture driver port  429  as will be described in  FIGS. 8A-8F . 
       FIG. 5  shows an illustrative test cartridge  402  of the type that does not include on-board diluent/reagents. Many of the functional components are identical to those illustrated with reference to test cartridge  401 , but instead of on-board diluent/reagents, test cartridge  402  has a reagent input port  460  adapted to be connected to an external source of diluent/reagent. Test cartridge  402  may be used in embodiments in which diluent/reagents that are needed for an analysis may be too costly to package individually or may require refrigerated storage. In such an embodiment, diluent/reagent may be provided from a source within cell analyzer  200  or from a reagent supply module. 
       FIG. 6  shows an illustrative reagent supply module  470  positioned to receive test cartridge  402 . The reagent supply module  470  includes a receiving area  473  for docking the test cartridge  402 , and contains a vessel for holding the diluent/reagent, a reagent metering pump adapted to pump the diluent/reagent, and a reagent output port  475 . The reagent output port  475  is constructed with a suitable shape and/or elastomeric materials to insure a liquid-tight connection to reagent input port  460  on the test cartridge  402 , when the test cartridge is docked to the reagent supply module  470 . Reagent supply module  470  has an opening  477  suitably sized to allow monitoring camera  255  ( FIG. 3 ) to image the rotary valve  415 . Additionally a window  478  in the reagent supply module  470  is constructed to align with the photometric chamber  409  in the test cartridge. Window  478  allows the photometric light source  293  and photometric detector  295  ( FIG. 3 ) to make optical absorbance measurements on the fluid within photometric chamber  409 . 
     In one embodiment, the size of the vessel within reagent supply module  470  is of sufficient capacity to provide diluent/reagents to dilute and/or stain from ten to about one-hundred samples with a diluent/reagent to sample ratio of 10:1 to about 250:1. The reagent supply module  470  further can include a self-priming mechanism for priming the liquid reagent and eliminating air bubbles. In such an embodiment, the reagent supply module  470  may include a chamber for collecting waste reagent from the priming process. Once the test cartridge  402  is docked with the reagent supply module  470  the combined pieces perform the same functions as test cartridge  401  except that the reagent supply module  470  replaces the blister pack  417 . Inside cell analyzer  200  the vacuum/pressure pump  240  makes connections through manifold  245  to sample driver port  411  and mixture driver port  429 . The interfaces between the manifold  245  and these ports are constructed with a suitable shape and/or elastomeric material to ensure an airtight connection so that system controller  250  can control movement of the fluids in the test cartridge (see  FIG. 3 ). In such an embodiment the presser foot  230  is not needed. 
     The only volume that is measured precisely is the metered volume of the original biological sample. Various means for metering a small volume of liquid are well known in the art. Two devices that are well suited for low cost, single use applications according to the present invention are shown in  FIG. 7A  and  FIG. 7B .  FIG. 7A  shows the face of a cylindrical valve stem  485  of a rotary face valve. Metering chamber  483  is formed in the face by highly precise manufacturing processes such as injection molding. The chamber  483  is narrow and tubular in shape and centered in the face of the cylindrical stem  485 . A slot  487  in the top of stem  485  acts as a valve indexer to indicate the position of the valve stem  485 . Also formed in the face of valve stem  485  is an auxiliary connector  421 , which has a circular shape. When assembled into the rotary valve  415  ( FIGS. 4 and 5 ), metering chamber  483  is able to connect between ports in the valve which are 180 degrees apart, while auxiliary connector  421  connects between other ports which are 60 degrees apart. As will be explained with reference to  FIG. 8A-8F , system controller  250  is able to control movement of the fluids by rotating valve stem  485  and by positioning the valve according to the valve indexer  487  according to preprogrammed sequences. Thus in a first position, the metering chamber  483  can be connected to the input port  407  ( FIG. 4  and  FIG. 5 ) and filled with the biological sample, and then by rotating valve stem  485 , the volume contained within metering chamber  483  can be isolated and transferred for analysis. 
       FIG. 7B  is a side view of a valve stem  485 ′ with a metering chamber formed as a pass-through conduit  413  in the tapered seat of valve stem  485 ′. Pass-through conduit  413  is able to connect with fluidic channels in rotary valve  415  which are 180 degrees apart. Also shown in  FIG. 7B  is auxiliary fluidic connector  421 ′, which provides connections to adjacent fluidic channels which are 60 degrees apart. 
     When assembled in the rotary valve  415  ( FIG. 4  and  FIG. 5 ) having a tapered seat to receive valve stem  485 ′, pass-through conduit  413  can be connected to input port  407  ( FIG. 4  and  FIG. 5 ), filled with the biological sample, and then by rotating valve stem  485 ′, the volume of sample contained within pass-through conduit  413  can be isolated and transferred for analysis.  FIG. 7B  also shows auxiliary fluidic connector  421 ′, which provides fluidic connections to adjacent fluidic channels on the test cartridge according to the position of the valve indexer  487 ′. It will be appreciated that the rotary face valve of  FIG. 7A  and the tapered seat valve of  FIG. 7B  are alternate embodiments for isolating sample and controlling fluidic paths. Therefore, in the descriptions that follow references to metering chamber  483  in a rotary face valve will be equally applicable to pass-through conduit  413  in a tapered seat valve. 
     Now turning our attention to  FIGS. 8A through 8F , and with reference to  FIG. 3 , a sequence of operations will be illustrated that enable cell analyzer  200  to perform automated microscopic cell analysis on a biological sample without skilled operator interactions. In  FIG. 8A  a sample is shown deposited into input port  407 , which is in fluid communication with rotary valve  415 . As illustrated in  FIG. 8A , the stem  485  ( FIG. 7A ) of rotary valve  415  is in a first position wherein the metering chamber  483  ( FIG. 7A ) is aligned with the sample input port  407  and the sample driver port  411 . A vacuum, supplied by the analyzer to sample driver port  411 , draws the sample from the input port  407  into the metering chamber  483  and into the photometric chamber  409 . When the photometric chamber  409  has been filled with sample, the system controller  250  ( FIG. 3 ) collects absorbance data from the undiluted sample using the photometric light source  293  ( FIG. 3 ) and photometric detector  295  ( FIG. 3 ). As will be understood by those skilled in the art, suitable choice of optical wavelengths and chamber geometry and analysis of the light passing through the biological sample can be used to determine concentrations of certain analytes in the sample such as hemoglobin. 
     By illustration and with reference to  FIG. 8B , cartridge  401  is shown with a diluent/reagent contained in a blister pack  417 . When rotary valve  415  positioned such that the metering chamber  483  is aligned with the input port  407  and photometric chamber  409 , auxiliary connector  421  provides a fluid communication path between the blister pack  417  and vent  423 . When pressure is applied to the blister pack  417  by presser foot  230  ( FIG. 3 ), diluent/reagent is released and flushed through auxiliary connector  421  thereby priming the channels and removing air bubbles through vent  423 . 
       FIG. 8C  shows rotary valve  415  turned counterclockwise 60 degrees to a second position, which isolates a predetermined amount of sample in the metering chamber  483 . In this second position the stem  485  of rotary valve  415  is positioned such that the metering chamber  483  is in fluid communication with blister pack  417  and the serpentine imaging chamber  403 . 
     In  FIG. 8D , the rotary valve  415  is shown in the same position as in  FIG. 8C  but following operation of the presser foot  230  which applies pressure to the blister pack  417 . As illustrated by the shaded area, the diluent/reagent from blister pack  417  and the isolated sample  493  from the metering chamber  483  are transferred into the imaging chamber  403 . A minimum volume of reagent of three times the volume of the pass-through conduit  413  is needed to flush the entire sample from the rotary valve  415 . According to the analysis being conducted, a sufficient volume of the reagent is pushed through the rotary valve  415  to completely wash out the isolated sample and to achieve the approximate dilution ratio desired. 
     In  FIG. 8E  the rotary valve  415  is shown turned counterclockwise 120 degrees from its previous position shown in  FIG. 8D  to its third position, wherein auxiliary connector  421  is aligned with mixture driver port  429  and imaging chamber  403 . Vacuum/pressure pump  240  of cell analyzer  200  ( FIG. 3 ) supplies pressure to mixture driver port  429  and pushes all of the mixture of sample and diluent/reagent from the imaging chamber  403  into passive mixing chamber  405 . As the mixture enters passive mixing chamber  405 , air within the chamber is vented through vent port  433 . Once all of the mixture of sample and diluent/reagent has been transferred to the passive mixing chamber  405 , vacuum/pressure pump  240  applies a controlled vacuum to mixture driver port  429  such that the mixture is pulled back into the imaging chamber  403 . A preprogrammed sequence of pushing the mixture into the passive mixing chamber  405  and pulling it back into the imaging chamber  403  is repeated to achieve a final mixture  495  that is free from cell clumping and overlapping after the cells settle to the bottom of the imaging chamber  403 . In the final movement of the mixture  495 , it is positioned entirely within the imaging chamber  403  as illustrated in  FIG. 8F . We have found that that in most instances, pushing the sample and diluent/reagent into mixing chamber  405  and pulling it out is sufficient to provide a uniform mixture. Further, the mixture remains substantially uniform when it is transferred into serpentine imaging chamber  403 . It should also be noted that the mixing chamber  405  could be located at the beginning of the imaging chamber  403 . 
       FIG. 8F  illustrates the final step of the sample preparation sequence. At this point in the preprogrammed sequence, the entire final mixture  495  has been withdrawn from the passive mixing chamber  405  and is positioned in the imaging chamber  403 . When this position is achieved, the rotary valve  415  is rotated counterclockwise approximately 30 degrees to the position shown in  FIG. 8F , whereby it is not in fluid communication with any fluidic channel in rotary valve  415 , thereby blocking further fluid communication with the imaging chamber  403  so that no further movement of the final mixture  495  can take place. 
       FIG. 9  shows a cross section of the passive mixing chamber  405 . The chamber is referred to as “passive” because as illustrated, it does not contain any active mixing element such as a bead or spin-bar. Such devices may be used in some embodiments, but we have found that an adequately sized chamber as depicted in  FIG. 9  is simpler and provides excellent mixing of the sample and reagent. In operation the diluent/reagent and sample  493  are driven by vacuum/pressure pump  240  ( FIG. 3 ) and enter and exit the chamber through mixing chamber opening  497 . As liquid enters the chamber, air within the chamber escapes through vent port  433 . The cross section of passive mixing chamber  405  illustrates wall geometry that increases smoothly in size from the bottom to the top such that the mixture entering from below expands into a larger volume. The chamber  405  may have asymmetrical sloped walls  484  and  491  to promote mixing of the sample and reagent and for removing bubbles from the mixture. After all of the mixture is in the chamber, air bubbles may be introduced to the chamber by vacuum/pressure pump  240  through mixing chamber opening  497 . These air bubbles further promote mixing and subsequently escape through vent port  433 . The choice of materials used to fabricate the passive mixing chamber  405  should take into consideration the wetting properties of the specific 1 diluent/reagent(s) being utilized in the test cartridge  401 . The properties of the material, among other requirements, should ensure that liquid surface tension will pull back all of the liquid in contact with the side walls of the chamber when the vacuum/pressure pump  240  empties the chamber through mixing chamber opening  497 . 
       FIG. 10  illustrates test cartridge  400  which comprises an imaging chamber  403  having at one end a sample input port  450 , and at the opposite end a vent  453 . A user of test cartridge  400  collects a small known volume of whole blood and mixes it manually with a diluent/reagent in a separate single-use sample preparation device (not shown). Once mixed, the entire mixed volume is injected into sample input port  450 . Air escapes through vent  453  as the mixture is injected allowing the sample to fill the imaging chamber  403 . The imaging chamber is essentially the same imaging chamber as described above and shown in  FIGS. 8A-8F . Test cartridge  400  can be placed into analyzer  200  ( FIG. 3 ) for analysis beginning at step  560  of  FIG. 11  as described below. 
     Turning our attention to  FIG. 11  we will now describe the overall operation of cell analyzer  200  configured to provide a “CBC with Differential” analysis with reference to the test cartridge  401  illustrated in  FIGS. 8A-8F  and cell analyzer  200  illustrated in  FIG. 3 . To obtain the blood sample from a patient presented at box  500 , the user first obtains a new test cartridge  401  at box  505  and opens it to expose the input port  407 . Blood from a finger prick is applied as illustrated in  FIG. 1  at box  510  and the input port  407  is covered. The user inserts the test cartridge into the cell analyzer  200  at box  515 . The test cartridge is moved into the analyzer where mechanical and fluid connections are made between the analyzer and the cartridge as described above with reference to  FIG. 3 . As a first step of analysis, the sample is drawn into the metering chamber passing through and into photometric chamber  409  ( FIG. 8A ). Absorbance of the blood is measured at box  520 . Data from absorbance measurements are used to determine hemoglobin concentration. At box  530  sample in the metering chamber  483  is imaged using monitoring camera  255  and analyzed to confirm that the metering chamber was properly filled at box  535 . If an error is detected the analysis is terminated at box  537  and the user is alerted to the error and instructed to remove the cartridge and reject the test. 
     If the pass-through conduit  413  is correctly filled the diluent/reagent channel is primed at box  540  as described above with reference to  FIG. 8B . Rotary valve  415  is then turned to the position shown in  FIG. 8C  to isolate the sample and to allow diluent/reagent to wash the metered volume of blood out of the pass-through conduit  413  at box  545  while being imaged by monitoring camera  255 . The transfer continues until the monitoring camera  255  confirms that diluent/reagent plus sample has almost filled the imaging chamber as illustrated in  FIG. 8D . 
     Once a sufficient volume of diluent/reagent is transferred, rotary valve  415  is positioned as shown in  FIG. 8E  and the total volume of sample and diluent/reagent is mixed at box  550 . At box  555  the entire volume  495  is transferred to the imaging chamber and rotary valve  415  is positioned as shown in  FIG. 8F . Note that by transferring the entire volume of mixed sample  495 , all of the metered volume of blood from the original sample plus the unmetered volume of diluent/reagent is positioned in the imaging chamber at box  555 . 
     If test cartridge  400  is used, it is inserted into cell analyzer  200  and analysis begins at step  560 . Analysis of test cartridge  401  or  402  continues at step  560  when the x-y stage  225  moves the test cartridge  401  to obtain bright-field and fluorescent images of the entire imaging chamber  403  at box  560 . In an alternate embodiment, objective lens  265  and/or digital camera  280  are moved and test cartridge  401  remains stationary. In yet another embodiment objective lens  265  has sufficient field of view to capture the entire imaging chamber  403  without movement. Two digital images of each physical frame of the imaging chamber are transferred to image processor/computer  290  at box  565 . One image, taken with bright-field optics, can be compared to the other image taken with fluorescent optics to identify red blood cells, white blood cells and platelets. Further analysis of the white cell sizes and internal structure can identify sub-types of white cells using pattern recognition. 
     At box  570  comparison of the bright-field and fluorescent images can differentiate mature red cells from reticulocytes and nucleated red blood cells. By dividing each cell count by the known volume of the metering chamber  483 , the concentration (cells per unit volume) can be determined. By using a sphering agent the planar sizes of red cells can be transformed into mean corpuscular volume (MCV). Combining the red blood cell count with MCV and the volume of the metering chamber  483  allows the calculation of hematocrit (HCT) and red cell distribution width (RDW). Further calculations using the separately measured HGB from box  525 , combined with the RBC count gives mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin content (MCHC). 
     At box  575  the measured results are compared with previously defined limits and ranges for the particular patient population and determination is made whether the results are within or outside normal expected ranges. According to this determination results within normal ranges are reported in box  580  and results that are outside the normal ranges are reported in box  585 . 
     EXAMPLES 
     Example 1: Information from Bright-Field and Fluorescent Optics 
       FIG. 12  shows images that were collected using test devices according to the present invention. A fluorescent stain Acridine Orange (AO) was used to differentially stain DNA and RNA of cells in a whole blood sample. The visual images of  FIG. 12  were obtained using an Olympus 20××0.4 NA objective lens  265  and a Basler 5 MP digital camera  280 . Excitation of the bright-field images in the second column was provided by white light bright-field source  260 . Excitation of the fluorescent images in the third column was a 455 nm blue fluorescent light source  270 . 
     White blood cells have significant RNA and DNA and therefore can be seen in the fluorescent images having green and orange structures. The size and shape of the green nuclear structure and overall size of the white cells can be used to differentiate them into sub-groups identified by name in the first column. Notably the basophil and eosinophil sub-groups of white cells have characteristic features in the bright-field image due to the presence of large granules in the cytoplasm. Therefore embodiments of the present invention make use of both bright-field and fluorescent image analysis to differentiate sub-groups of white cells. 
     Platelets also take up the AO stain but the size of a platelet is significantly smaller than any white cell and can therefore be differentiated. Because red cells lose their nucleus as they mature, they do not have nuclear material to take up the AO stain. Consequently the red cells can be identified as the objects that appear in the bright-field and cannot be seen in the fluorescent field. The immature red cells, called reticulocytes and the nucleated red blood cells (nRBC) have attributes of red cells but also show small levels of fluorescence. Embodiments of the present invention make use of these combined attributes to identify and sub-group red blood cells. 
     Example 2. Statistical Sampling of the Imaging Chamber 
     Table 1 illustrates a comparison of CBC parameters obtained according to the present invention and from an automated hematology analyzer. 
                                                                                                   TABLE 1               Column 1   # pairs   RBCs   WBCs   ROI   RBC/f   RBC/f(%)-   WBC/f   WBC/f(%)   RBC/WBC                                100%   9916   2455492   5125   3818.7   643.02   100.0   1.342   100.0   479.12        50%   4958   1229669   2535   1913.7   642.56   99.9   1.325   98.7   485.08        25%   2479   623048   1285   968.5   643.28   100.0   1.327   98.9   484.86        10%   992   242197   519   373.5   648.48   100.8   1.390   103.5   466.66        5%   496   126186   262   197.2   639.82   99.5   1.325   99.0   481.63        1%   100   23683   63   35.6   664.61   103.4   1.768   131.7   375.92                    
Sample: Low WBC count—approximately 2000/uL (normal is 3,000-10,000/uL).
 
Magnification: 20×
 
Number of images: approximately 10,000 bright-field and 10,000 fluorescent
 
Variable: Column 1—Percentage of total cells use in the calculation
 
Column # pairs—the number of pairs of images (bright-field plus fluorescent)
 
Column RBCs—total number of Red Blood Cells counted
 
Column WBCs—total number of White Blood Cells counted
 
Column ROI—total Region of Interest. This is the ‘effective’ number of image frames occupied by actual sample. A frame totally filled with sample/cells is “1”. A partial frame (due to an edge or the curved ends of the serpentine shape), is a fraction of a frame (e.g. 0.567).
 
Column RBC/f—Average number of Red Blood Cells per frame (Column RBCs divided by Column 5 ROI).
 
Column RBC/f(%)—This is the RBC/frame value at a particular sampling percentage divided by the RBC/frame for the 100% sampling case (top line). This is an estimate of the accuracy of the particular sampling percentage compared to counting 100% of the cells.
 
Column WBC/f—Average number of White Blood Cells per frame (Column WBCs divided by Column ROI).
 
Column 9 WBC/f(%)—This is similar to Column 7 but estimates the accuracy of the sampling percentage for the White Blood Cells.
 
Column RBC/WBC—This is the ratio of RBC/WBC for the particular sampling percentage.
 
Results: A small percentage of the total frames can provide accurate results. As a smaller fraction of the total frames are counted, the accuracy is maintained down to 1% for Red Blood Cells and down to 5% for White Blood Cells.
 
Discussion: In these experiments, it took approximately one second to capture an image pair. For this experiment, where almost 10,000 image pairs were needed to capture 100% of the sample, this means that image analysis took 10,000 seconds or approximately 2.8 hours. The experiment shows that the uniformity of the distribution of cells across the imaging chamber was good enough to provide accurate results by counting cells in only 5% of the frames. The goal of “counting every cell” is achieved because the entire sample size (the Region of Interest ROI) is measured, but only 5% of the images need to be analyzed to get accurate results. This reduces the image analysis time to approximately 8 minutes. It is expected that advances in camera and computer processing technology will further reduce this time.
 
     The present invention has now been described in connection with a number of specific embodiments thereof. However, numerous modifications which are contemplated as falling within the scope of the present invention should now be apparent to those skilled in the art. Therefore, it is intended that the scope of the present invention be limited only by the scope of the claims appended hereto. In addition, the order of presentation of the claims should not be construed to limit the scope of any particular term in the claims.