Abstract:
A blood analyzer, comprising a sample preparing part; a flow cell; a light source; a scattered light detector for detecting scattered light from a measurement sample irradiated by the light source; a fluorescence light detector comprising an avalanche photo diode for detecting fluorescence light from the measurement sample irradiated by the light source; a signal processing part for processing a first detection signal from the scattered light detector and a second detection signal from the fluorescence light detector, wherein the signal processing part reduces high frequency noise included in an amplified second detection signal; and a analysis part for classifying white blood cells in the blood into groups based on the first and the second detection signals processed by the signal processing part is disclosed. A blood analyzing method is also disclosed.

Description:
[0001]     This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. JP2005-329919 filed Nov. 15, 2005, the entire content of which is hereby incorporated by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a blood analyzer and method for analyzing blood sample.  
       BACKGROUND  
       [0003]     A blood analyzer, which includes an optical flow cytometer, for analyzing a blood sample is known. The flow cytometer is provided with a flow cell for conducting the liquid of the blood sample, a light source for irradiating light onto the flow cell, and a light receiving element, and the light irradiated from the light source is scattered by the particles in the flow cell. The hemolyzing process of the red blood cells and the staining process of the particles of the white blood cells and the like are performed by adding hemolytic agent and fluorescence reagent to the blood sample, and the stained particles emit fluorescence light when receiving light. The scattered light and the fluorescence light are received by the light receiving elements, and the detection signals thereof are analyzed to measure the white blood cells in the blood sample and to classify the white blood cells to lymphocytes, monocytes, granulocytes and the like. In such flow cytometer, since the classification of the white blood cells and the ghosts (red blood cell membrane not completely shrunk with hemolytic agent) is discriminated using the fluorescent light signal, the hemolytic agent having high hemolyzing ability of shrinking the red blood cells to an extent the sizes of the white blood cells and the ghost can be clearly distinguished does not need to be used and thus the extent of damage of the white blood cells is alleviated and the form of the white blood cells is maintained. The reagent for dissolving the red blood cells while maintaining the form of the white blood cells to have the blood sample in a state suitable for the classification of the white blood cells has been disclosed (see U.S. Pat. No. 6,004,816).  
         [0004]     Furthermore, an optical system of high measurement accuracy becomes necessary since the classification of the white blood cells by means of the flow cytometer is performed based on the slight difference in size and form of the cell or the nucleus of each white blood cell. Moreover, the optical system of high measurement accuracy is necessary to discriminate the white blood cells and the ghosts using the fluorescent light signal since some ghosts are attached with a small amount of fluorescent pigment and thus emit fluorescent light signal. A photo-multiplier (photoelectron multiplier) having high sensitivity is generally used as the fluorescent light receiving element (see e.g., U.S. Pat. No. 6,365,106). Furthermore, a flow cytometer using an avalanche photodiode (APD) as the light receiving element for receiving fluorescent light is also disclosed (see U.S. Pat. No. 5,739,902).  
         [0005]     The amplification ratio of the signal of the element itself is low in the avalanche photodiode compared to the photo-multiplier, and thus the gain of the amplifying circuit arranged in the post-stage of the element must be set large. However, if the output signal of the avalanche photodiode is amplified with the amplifying circuit set with a large gain, the level of high frequency noise generated in the amplifying circuit increases, and high precision analysis of the sample becomes difficult.  
       BRIEF SUMMARY  
       [0006]     The scope of the present invention is defined solely by the appended claims, and is not affected to any degree by the statements within this summary.  
         [0007]     A first aspect of the present invention is a blood analyzer, comprising: a sample preparing part for preparing a measurement sample comprising a blood, a hemolyzing reagent, and a staining reagent; a flow cell in which the measurement sample flows; a light source for irradiating the measurement sample flowing in the flow cell; a scattered light detector for detecting scattered light from the measurement sample irradiated by the light source; a fluorescence light detector comprising an avalanche photo diode for detecting fluorescence light from the measurement sample irradiated by the light source; a signal processing part for processing a first detection signal from the scattered light detector and a second detection signal from the fluorescence light detector, wherein the signal processing part reduces high frequency noise included in an amplified second detection signal; and a analysis part for classifying white blood cells in the blood into groups based on the first and the second detection signals processed by the signal processing part.  
         [0008]     A second aspect of the present invention is a blood analyzer, comprising: a sample preparing part for preparing a measurement sample comprising a blood, a hemolyzing reagent, and a staining reagent; a flow cell in which the measurement sample flows; a light source for irradiating the measurement sample flowing in the flow cell; a scattered light detector for detecting scattered light from the measurement sample irradiated by the light source; a fluorescence light detector comprising an avalanche photo diode for detecting fluorescence light from the measurement sample irradiated by the light source; a signal processing part for processing a first detection signal from the scattered light detector and a second detection signal from the fluorescence light detector, wherein the signal processing part comprises a low pass filter for reducing high frequency noise included in an amplified second detection signal; and a analysis part for classifying white blood cells in the blood into groups based on the first and the second detection signals processed by the signal processing part; wherein a cutoff frequency of the low pass filter is less than frequency Y of following formula:
 
 Y= 17.289EXP (−0.022 C )+2
 
         [0009]     (C represents electric capacity between terminals of the avalanche photo diode).  
         [0010]     A third aspect of the present invention is a blood analyzing method, comprising: preparing a measurement sample comprising a blood, a hemolyzing reagent, and a staining reagent; exposing the measurement sample to light from a light source; detecting scattered light from the measurement sample irradiated by the light source; detecting, by an avalanche photo diode, fluorescence light from the measurement sample irradiated by the light source; processing a first detection signal obtained from the scattered light; processing a second detection signal obtained from the fluorescence light, the processing of the second detection signal comprising reducing high frequency noise included in an amplified second detection signal; and classifying white blood cells in the blood into groups based on a processed first detection signal and a processed second detection signal. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
         [0012]      FIG. 1  is a front view briefly showing the structure of the sample analyzer of an embodiment;  
         [0013]      FIG. 2  is a perspective exterior view of the measurement unit provided in the sample analyzer of the embodiment;  
         [0014]      FIG. 3  is a perspective view showing the internal structure of the measurement unit provided in the sample analyzer of the embodiment;  
         [0015]      FIG. 4  is a side view showing the internal structure of the measurement unit provided in the sample analyzer of the embodiment;  
         [0016]      FIG. 5  is a block diagram showing the structure of the measurement unit provided in the sample analyzer of the embodiment;  
         [0017]      FIG. 6  is a fluid circuit diagram showing the structure of the sample supply section provided in the measurement unit;  
         [0018]      FIG. 7  is a perspective view schematically showing the structure of the flow cell provided in the measurement unit;  
         [0019]      FIG. 8  is a brief plan view schematically showing the structure of the flow cytometer provided in the measurement unit;  
         [0020]      FIG. 9  is a scattergram prepared using the blood analyzer according to the embodiment;  
         [0021]      FIG. 10  is a block diagram showing a schematic configuration of the signal processing circuit shown in  FIG. 5 ;  
         [0022]      FIG. 11  is a frame format view explaining the range used in the analysis of the amplified signal of the side fluorescent light signal;  
         [0023]      FIG. 12  is a scattergram obtained when the maximum allowable level of noise is set to 80 mVp-p;  
         [0024]      FIG. 13  is a scattergram obtained when the maximum allowable level of noise is set to 100 mVp-p;  
         [0025]      FIG. 14  is a scattergram obtained when the maximum allowable level of noise is set to 150 mVp-p;  
         [0026]      FIG. 15  is a scattergram obtained when the maximum allowable level of noise is set to 200 mVp-p;  
         [0027]      FIG. 16  is a scattergram obtained when the maximum allowable level of noise is set to 250 mVp-p;  
         [0028]      FIG. 17  is a scattergram obtained when the maximum allowable level of noise is set to 300 mVp-p;  
         [0029]      FIG. 18  is a scattergram obtained when the maximum allowable level of noise is set to 400 mVp-p;  
         [0030]      FIG. 19  is a scattergram obtained when the maximum allowable level of noise is set to 500 mVp-p;  
         [0031]      FIG. 20  is a scattergram obtained when the maximum allowable level of noise is set to 600 mVp-p;  
         [0032]      FIG. 21  is a scattergram obtained when the maximum allowable level of noise is set to 700 mVp-p;  
         [0033]      FIG. 22  is a graph showing the relationship between the inter-terminal capacity of the avalanche photodiode and the high pass cut-off frequency of the A/D converter when the maximum allowable level of noise is set to 300 mVp-p; and  
         [0034]      FIG. 23  is a graph showing the relationship between the inter-terminal capacity of the avalanche photodiode and the high pass cut-off frequency of the A/D converter when the maximum allowable level of noise is set to 500 mVp-p.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]     The preferred embodiments of the present invention are described hereinafter with reference to the drawings.  
         [0036]      FIG. 1  is a front view briefly showing the structure of the sample analyzer of an embodiment. As shown in  FIG. 1 , a sample analyzer  1  of the present embodiment is used in blood testings, comprises a measurement unit  2  and data processing unit  3 . The measurement unit  2  performs predetermined measurements of components contained in blood specimens, and the measurement data are subjected to an analysis process when received by the data processing unit  3 . The sample analyzer  1  is installed in medical facilities such as hospitals, or pathology laboratories and the like. The measurement unit  2  and data processing unit  3  are connected by a data transfer cable  3   a  so as to be capable of mutual data communications. The configuration is not limited to a direct connection between the measurement unit  1  and data processing unit  3  by the data transfer cable  3   a , inasmuch as, for example, the measurement unit  2  and data processing unit  3  may also be connected through a dedicated line using a telephone line, or a communication network such as a LAN, Internet or the like.  
         [0037]      FIG. 2  is a perspective view of the exterior of the measurement unit  2 . As shown in  FIG. 2 , at the lower right of the front of the measurement unit  2 , is provided with a blood collection tube placement unit  2   a  for placing a blood collection tube  20  that contains a blood sample. The blood collection tube placement unit  2   a  can receive a blood collection tube  20  placed therein by a user when a button switch  2   b  provided nearby is pressed by the user and the blood collection tube placement unit  2   a  moves in a forward direction. After the blood collection tube  20  has been placed, the user again presses the button switch  2   b  and the blood collection tube placement unit  2   a  withdraws and closes.  
         [0038]      FIG. 3  is a perspective view showing the interior structure of the measurement unit  2 , and  FIG. 4  is a side view of the same. The blood collection tube placement unit  2   a  holding the collection tube  20  is received within the measurement unit  2  as previously described, and the collection tube  20  is positioned at a predetermined suction position. A sample supply unit  4  including a pipette  21  for suctioning samples, chambers  22  and  23  for mixing and adjusting blood and reagent and the like is provided within the measurement unit  2 . The pipette  21  is tube-like and extends vertically, and the tip is sharply tapered. The pipette  21  is linked to a syringe pump not shown in the drawing, and a predetermined amount of liquid can be suctioned or discharged by the operation of this syringe pump; the pipette  21  is also linked to a moving mechanism so as to be movable in vertical directions and forward and backward directions. The blood collection tube  20  is sealed by a rubber cap  20   a , and the sharp tip of the pipette  21  pieces the cap  20   a  of the collection tube  20  placed at the suction position, and a predetermined amount of blood sample contained in the collection tube  20  can be suctioned by the pipette  21 . As shown in  FIG. 4 , chambers  22  and  23  are provided behind the collection tube placement unit  2   a ; the pipette  21  is moved by the moving mechanism when the blood sample has been suctioned, and supplies the blood sample to the chambers  22  and  23  by discharging the blood sample into the chambers  22  and  23 .  
         [0039]      FIG. 5  is a block diagram showing the structure of the measurement unit  2 , and  FIG. 6  is a flow circuit diagram showing the structure of the sample supply unit  4 . As shown in  FIG. 4 , the measurement unit  2  is provided with a sample supply unit  4 , WBC detection unit  5 , RBC detection unit  6 , HGB detection unit  7 , control unit  8 , and communication unit  9 . The control unit  8  is configured by a CPU, ROM, RAM and the like, and performs operation control of each type of structural element of the measurement unit  2 . The communication unit  9  is an interface, such as, for example, an RS-232C interface, USB interface, Ethernet (registered trademark), and is capable of sending and receiving data to/from the data processing unit  3 .  
         [0040]     As shown in  FIG. 6 , the sample supply unit  4  is a flow unit provided with a plurality of electromagnetic valves, diaphragm pumps and the like. Chamber  22  is used to prepare the sample supplied for the measurement of red blood cells and platelets, and the measurement of hemoglobin. The chamber  23  is used to prepare the sample supplied for white blood cell measurement.  FIG. 6  shows only the structure of the flow circuit on the periphery of the chamber  23  in order to simplify the drawing. The chamber  23  is connected to a reagent container FFD accommodating hemolytic agent and a reagent container FFS accommodating staining fluid through fluid flow paths P 1  and P 2 , such as tubes or the like. Electromagnetic valves SV 19  and SV 20  are provided in the fluid flow path P 1  connecting the chamber  23  and the reagent container FFD, and a diaphragm pump DP 4  is provided between the electromagnetic valves SV 19  and SV 20 . The diaphragm pump DP 4  is connected to a positive pressure source and a negative pressure source, such that the diaphragm pump DP 4  can be operated by positive pressure drive and negative pressure drive. Electromagnetic valves SV 40  and SV 41  are provided in the fluid flow path P 2  connecting the chamber  23  and the reagent container FFS, and a diaphragm pump DP 5  is provided between the electromagnetic valves SV 40  and SV 41 .  
         [0041]     The electromagnetic valves SV 19 , SV 20 , SV 40 , SV 41 , and diaphragm pumps DP 4  and DP 5  are operationally controlled as follows, and are capable of supplying hemolytic agent and staining fluid to the chamber  23 . First, the electromagnetic valve SV 19 , which is disposed on the reagent container FFD side of the diaphragm pump DP 4 , is opened, and with the electromagnetic valve SV 20 , which is disposed on the chamber  23  side of the diaphragm pump DP 4 , in the closed state, a hemolytic agent is supplied in a fixed dosage from the reagent container FFD by negative pressure actuation of the diaphragm pump DP 4 . Thereafter, the electromagnetic valve SV 19  is closed, the electromagnetic valve SV 20  is opened, and the fixed quantity of hemolytic agent is supplied to the chamber  23  by positive pressure actuation of the diaphragm pump DP 4 . Similarly, the electromagnetic valve SV 40 , which is disposed on the reagent container FFS side of the diaphragm pump DP 5 , is opened, and with the electromagnetic valve SV 41 , which is disposed on the chamber  23  side of the diaphragm pump DP 5 , in the closed state, a staining fluid is supplied in a fixed dosage from the reagent container FFS by negative pressure actuation of the diaphragm pump DP 5 . Thereafter, the electromagnetic valve SV 40  is closed, the electromagnetic valve SV 41  is opened, and the fixed quantity of staining fluid is supplied to the chamber  23  by positive pressure actuation of the diaphragm pump DP 5 . Thus, the blood sample and reagents (hemolytic reagent and staining fluid) are mixed and the sample is prepared for white blood cell measurement.  
         [0042]     Furthermore, the chamber  23  is connected to the WBC detection unit flow cytometer through a fluid flow path P 3  that includes tubes and an electromagnetic valve SV 4 . The fluid flow path P 3  branches in its medial region, and electromagnetic valves SV 1  and SV 3  are connected in series at the branch. A syringe pump SP 2  is disposed medially to the electromagnetic valves SV 1  and SV 3 . A stepping motor M 2  is connected to the syringe pump SP 2 , such that the syringe pump SP 2  is actuated by the operation of the stepping motor M 2 . Furthermore, the fluid flow path P 3  connecting the chamber  23  and the WBC detection unit  5  also branches, and an electromagnetic valve SV 29  and diaphragm pump DP 6  are connected at the branch. When white blood cells are measured by the WBC detection unit  5 , the diaphragm pump DP 6  is operated under negative pressure with the electromagnetic valves SV 4  and SV 29  in an open state, and the sample charges the fluid flow path P 3  when the sample is suctioned from the chamber  23 . When the sample charging is completed, the electromagnetic valves SV 4  and SV 29  are closed. Thereafter, the electromagnetic valve SV 3  is opened, and the charged sample is supplied to the WBC detection unit  5  by operating the syringe pump SP 2 .  
         [0043]     As shown in  FIG. 6 , the sample supply unit  4  is provided with a sheath fluid chamber  24 , and the sheath fluid chamber  24  is connected to the WBC detection unit  5  through the fluid flow path P 4 . An electromagnetic valve SV 31  is provided in the fluid flow path P 4 . The sheath fluid chamber  24  is a chamber for storing sheath fluid to be supplied to the WBC detection unit  5 , and is connected to the sheath fluid container EPK that holds the sheath fluid through the fluid flow path P 5  that includes tubes and an electromagnetic valve SV 33 . Before starting the measurement of white blood cells, the electromagnetic valve SV 33  is opened and sheath fluid is supplied to the sheath fluid chamber  24 , such that sheath fluid is stored in the sheath fluid chamber  24  beforehand. Then, when the measurement of white blood cells begins, the electromagnetic valve SV 31  is opened, and sheath fluid stored in the sheath fluid chamber  24  is supplied to the WBC detection unit  5  simultaneously with the sample supplied to the WBC detection unit  5 .  
         [0044]     The WBC detection unit  5  is an optical type flow cytometer, and is capable of measuring white blood cells by a flow cytometry via a semiconductor laser. The WBC detection unit  5  is provided with a flow cell  51 , which forms the fluid flow of the sample.  FIG. 7  is a perspective view schematically showing the structure of the flow cell  51 . The flow cell  51  is configured by a material such as transparent glass, glass, synthetic resin and the like, formed in a tube-like shape, and is a flow path through the interior of which the sheath fluid flows. The flow cell  51  is provided with an orifice  51  a, the internal cavity of which has an aperture that is narrower than the other parts. The vicinity of the inlet of the orifice  51  a of the flow cell  51  has a double-tube structure, and the internal side of this tube part becomes a sample nozzle  51   b . The sample nozzle  51   b  is connected to the fluid flow path P 3  of the sample supply unit  4 , and sample is discharged through the sample nozzle  51   b . Furthermore, the cavity on the outer side of the sample nozzle  51   b  is the flow path  51   c  through which the sheath fluid flows, and the flow path  51   c  is connected to the previously described fluid flow path P 4 . The sheath fluid supplied from the sheath fluid chamber  24  flows through the flow path  51   c  via the fluid flow path P 4 , and is introduced to the orifice  51   a . The sheath fluid supplied to the flow cell  51  in this way flows so as to encapsulate the sample discharged from the sample nozzle  51   b . Then, the sample flow is constricted by the orifice  51   a , such that the particles of white blood cells and red blood cells contained in the sample are encapsulated in the sheath fluid and pass through the orifice  51   a  one by one.  
         [0045]      FIG. 8  is a brief plan view that schematically shows the structure of the WBC detection unit  5 . A semiconductor laser light source  52  is arranged in the WBC detection unit  5  so as to emit laser light toward the flow cell  51 . An illumination lens system  53  including a plurality of lenses is arranged medially to the flow cell  51  and the semiconductor laser light source  52 . Parallel beams emitted from the semiconductor laser light source  52  are collected at a beam spot by the illumination lens system  53 . Furthermore, a beam stopper  54   a  is provided on the optical axis extending linearly from the semiconductor laser light source  52  so as to be opposite the illumination lens system  53  and with the flow cell  51  interposed therebetween. A photodiode  54  is arranged on the optical axis downstream of the beam stopper  54   a.    
         [0046]     When the sample flows through the flow cell  51 , optical signals of scattered light and fluorescent light are generated by the laser light. Among these, the forward scattered light signals irradiate toward the photodiode  54 . Among the light advancing along the optical axis extending linearly from the semiconductor laser  52 , the direct light of the semiconductor laser  52  is blocked by the beam stopper  54   a , and only the scattered light (hereinafter referred to as “forward scattered light”) advancing along the optical axis direction enters the photodiode  54 . The forward scattered light emitted from the flow cell  51  is subjected to photoelectric conversion by the photodiode  54 , and the electrical signals (hereinafter referred to as “forward scattered light signals”) generated by this conversion are amplified by an amplifier  54   b , and output to the control unit  8 . The forward scattered light signals reflect the size of the blood cells, and the size of the blood cells and the like can be obtained when the control unit  8  subjects the forward scattered light signals to signal processing.  
         [0047]     Furthermore, a side collective lens  55  is arranged at the side of the flow cell  51 , in a direction perpendicular to the optical axis extending linearly from the semiconductor laser light source  52  to the photodiode  54 , and the lateral light (light emitted in a direction intersecting the optical axis) generated when the semiconductor laser irradiates the blood cells passing through the flow cell  51  is collected by the side collective lens  55 . A dichroic mirror  56  is provided on the downstream side of the side collective lens  55 , and the signal light transmitted from the side collective lens  55  is divided into a scattered light component and fluorescent light component by the dichroic mirror  56 . A side scattered light photoreceptor photodiode  57  is provided at the side (the direction intersecting the direction of the optical axis connecting the side collective lens  55  and the dichroic mirror  56 ) of the dichroic mirror  56 , and an optical filter  58   a  and avalanche photodiode  58  are provided on the optical axis on the downstream side of the dichroic mirror  56 . Then, the side scattered light component separated by the dichroic mirror  56  is subjected to photoelectric conversion by the photodiode  57 , and the electrical signals (hereinafter referred to as “side scattered light signals”) generated by this conversion are amplified by an amplifier  57   a  and output to the control unit  8 . The side scattered light signals reflect the internal information (size of the nucleus and the like) of the blood cells, and the size of the nucleus of the blood cell and the like can be obtained when the control unit  8  subjects the side scattered light signal to signal processing. Furthermore, the side fluorescent light component emitted from the dichroic mirror  56  is subjected to wavelength selection by the optical filter  58   a , and subsequent photoelectric conversion by the avalanche photodiode  58 , and the electrical signals (side fluorescent light signals) thus obtained are amplified by an amplifier  58   b  and output to the control unit  8 . The side fluorescent light signals reflect information related to the degree of staining of the blood cells, and the stainability of the blood cells can be obtained by subjecting the side fluorescent light signals to signal processing.  
         [0048]     The RBC detection unit  6  can measure the number of red blood cells and platelets by a sheath flow DC detection method. The RBC detection unit  6  has a flow cell, and sample is supplied from the previously mentioned chamber  22  to the flow cell. When measuring red blood cells and platelets, a sample is prepared by mixing solution fluid with the blood in the chamber  22 . The sample is supplied from the sample supply unit to the flow cell together with the sheath fluid, and a flow is formed in which the sample is encapsulated in the sheath fluid within the flow cell. Furthermore, an aperture with an electrode is provided in the flow path in the flow cell, and the direct current (DC) resistance in the aperture is detected when the blood cells in the sample pass thought the aperture one by one, and the electrical signal of the DC resistance is output to the control unit  8 . since the DC resistance increases when the blood cell passes through the aperture, the electrical signal reflects information of the passage of the blood cell through the aperture, and the red blood cells and platelets can be counted by subjecting the electrical signals to signal processing.  
         [0049]     The HGB detection unit  7  is capable of measuring the amount of hemoglobin by the SLS hemoglobin method. The HGB detection unit  7  is provided with a cell for accommodating dilute sample, sample is supplied from the chamber  22  to this cell. When measuring hemoglobin, a sample is prepared by mixing dilution liquid and hemolytic reagent in blood in the chamber  22 . The hemolytic reagent has the characteristic of transforming hemoglobin in the blood to SLS hemoglobin. Furthermore, a light-emitting diode and photodiode are arranged in opposition with the cell interposed therebetween, and light emitted from the light-emitting diode is received by the photodiode. The light-emitting diode emits light of a wavelength that has high absorption by SLS hemoglobin, and the cell is formed of a plastic material of high transparency. Thus, in the photodiode, only the transmission light absorbed by the dilute sample is received among the light emitted by the light-emitting diode. The photodiode outputs electrical signals corresponding to the amount of received light (optical density) to the control unit  8 , and the control unit  8  compares this optical density with the optical density of the dilution liquid alone which was measured beforehand, then calculates the hemoglobin value.  
         [0050]     The control unit  8  receives electrical signals from the WBC detection unit  5 , the RBC detection unit  6 , and the HGB detection unit  7 , and obtains the measurement data indicating the size of the blood cells, the size of the nucleus of the blood cells, the stainability of the blood cells, the number of red blood cells, the number of blood platelets, the hemoglobin value and the like. As shown in  FIG. 5 , the control unit  8  includes a signal processing circuit  8   a  and a control circuit  8   b , where the output signal (side fluorescent light signal, forward scattered light signal, side scattered light signal) of the WBC detection unit  5 , the output signal of the RBC detection unit  6 , and the output signal of the HGB detection unit  7  are respectively signal processed by the signal processing circuit  8   a  to acquire the measurement data, and the measurement data is transmitted to the data processing unit  3  by the control circuit  8   b.    
         [0051]     The data processing unit  3  is configured by a computer provided with a CPU, ROM, RAM, hard disk, communication interface, input unit including a keyboard and mouse and the like, and a display device. The communication interface is, for example, an RS-232C interface, USB interface, Ethernet (registered trademark), and is capable of sending and receiving data to/from the measurement unit  2 . Furthermore, an operating system, and application program for analyzing the measurement data received from the measurement unit  2  are installed on the hard disk of the data processing unit  3 . In the data processing unit  3 , measurement data are analyzed, white blood cell count (WBC), red blood cell count (RBC), hemoglobin amount (HGB), hematocrit value (HCT, mean red blood cell volume (MCV), mean red blood cell hemoglobin (MCH), mean red blood cell hemoglobin concentration (MCHC), platelet count (PLT), are calculated, and a scattergram is prepared using the side scattered light signals and side fluorescent light signals, and the white blood cells are classifies as neutrophils, lymphocytes, monocytes, eosinophils, and basophils when the CPU executes the application program.  
         [0052]      FIG. 9  is a scattergram prepared using the blood analyzer according to the present embodiment. In  FIG. 9 , the vertical axis shows the intensity of the side fluorescent light (level of received light), and the horizontal axis shows the intensity of the side scattered light (level of received light). In the present experiment, measurement is performed using the same normal blood sample. The blood analyzer  1  according to the present embodiment has a configuration of classifying the white blood cells into five classification of neutrophils, lymphocytes, monocytes, eosinophils, and basophils all at once, where each cluster of neutrophils, lymphocytes, monocytes, eosinophils, and basophils is clearly formed in the scattergram prepared by the blood analyzer  1 , as shown in  FIG. 9 , indicating that the white blood cells are classified at high precision.  
         [0053]     The configuration of the signal processing circuit  8   a  of the control unit  8  will now be further described in detail.  FIG. 10  is a block diagram showing a schematic configuration of the signal processing circuit  8   a  shown in  FIG. 5 . As shown in  FIG. 10 , the signal processing circuit  8   a  includes amplifiers  81   a  to  81   c , signal processing filters  82   a  to  82   c , and AD converters  83   a  to  83   c . The signal processing filters  82   a  to  82   c  respectively includes low pass filters (high cut filters)  84   a  to  84   c  for reducing the high frequency noise, high pass filters  85   a  to  85   c  for reducing the fluctuation at the baseline of the signal, and baseline adjusting units  86   a  to  86   c  for adjusting the baseline of the signal to a predetermined level. The side fluorescent light signal output from the WBC detection unit  5  is processed by the amplifier  81   a , the signal processing filter  82   a , and the AD converter  83   a ; the forward fluorescent light signal output from the WBC detection unit  5  is processed by the amplifier  81   b , the signal processing filter  82   b , and the AD converter  83   b ; and the side scattered light signal output from the WBC detection unit  5  is processed by the amplifier  81   c , the signal processing filter  82   c , and the AD converter  83   c . Only the circuits for processing the output signals from the WBC detection unit  5  are shown in  FIG. 10  to simplify the explanation, but circuits for processing the output signals of the RBC detection unit  6  and the HGB detection unit are also arranged in the signal processing circuit  8   a.    
         [0054]     The set value of gain of the amplifiers  81   a  to  81   c  is switched by the measurement mode (white blood cell classifying mode, reticular red blood cell measurement mode etc.) The gain adjustment is performed by adjusting the gain so that the standard particles appear at the appropriate appearing position when the standard particles (e.g., control blood, calibrator), whose appearing position on the scattergram is known in advance in an appropriately gain adjusted state, are being measured. The low pass filters  84   a  to  84   c  are set with an appropriate high pass cut-off frequency so as to efficiently attenuate the noise of the side fluorescent light signal, the forward scattered light signal, and the side scattered light signal. For example, the high pass cut-off frequency of the low pass filter  84   a  is set to less than or equal to the frequency Y obtained by equation (5).
 
 Y= 10.482EXP(−0.018 C )+1.3  (eq.5)
 
         [0055]     C: inter-terminal capacity of avalanche photodiode  
         [0056]     This is based on the following knowledge of the inventors of the present invention.  FIG. 11  is a frame format view explaining the range used in the analysis of the amplified signal of the side fluorescent light signal. As shown in  FIG. 11 , the full scale input voltage of the AD converter  83   a  is 4V, and the resolution is 8 bits in the blood analyzer  1  according to the present embodiment. The resolution on the vertical axis of the scattergram for white blood cell classification described above is  250  where the top six stages out of the data of  256  stages obtained from the output of the AD converter  83   a  are excluded. That is, the range using the output voltage of the amplifier  81   a  in the analysis of the data processing unit  3  is 250×4000/256=3906.25 mV. The inventors of the present invention performed experiments with a plurality of high pass cut-off frequencies of the low pass filter  84   a  set in the above condition, and researched to what extent the maximum allowable level of the noise contained in the signal after the noise reduction by the low pass filter  84   a  should be set to obtain a satisfactory analysis result. FIGS.  12  to  21  are scattergrams obtained for when the maximum allowable level is 80 mV-p, 100 mVp-p, 150 mVp-p, 200 mVp-p, 250 mVp-p, 300 mVp-p, 400 mVp-p, 500 mVp-p, 600 mVp-p and 700 mVp-p. In FIGS.  12  to  21 , the regions enclosed with a solid line respectively show the respective regions in which neutrophils, lymphocytes, monocytes, eosinophils, and basophils are present. When the level of noise is 300 mVp-p, the overlap of the regions in which neutrophils, lymphocytes, monocytes, eosinophils, and basophils are present is small, and the white blood cells can be satisfactorily classified into five classifications with the noise level of such extent. In other words, an extremely satisfactory analysis is possible if the maximum allowable level of the noise contained in the amplified voltage is less than or equal to about 8% (100×300/3906.25=7.68%) with respect to the range (3906.25 mV) using the output voltage (amplified voltage) of the amplifier  81   a  in the analysis of the data processing unit  3 .  
         [0057]     The region in which the lymphocytes are present overlaps the region in which the ghosts are present, as shown in  FIGS. 20 and 21 , when the maximum allowable level of noise is greater than or equal to 600 mVp-p, but the region in which the lymphocytes are present and the region in which the ghosts are present do not overlap for 500 mVp-p, as shown in  FIG. 19 . High stainability is ensured while damaging the white blood cells to an appropriate extent and maintaining the form of the white blood cells with hemolytic agent in which the hemolyzing ability is not very high such as stromatolyser  4 DS and stromatolyser  4 DL, but the region in which the ghosts are present and the region in which the lymphocytes are present overlap and cannot be satisfactorily discriminated only with the side scattered light since the dissolving extent of the red blood cells is low. Therefore, in the classification of the white blood cells, accurate discrimination of the relevant lymphocytes and the ghosts is particularly important, and the respective appearing positions in the side fluorescent light intensity desirably do not overlap in order to discriminate the lymphocytes and the ghosts at high precision using the side fluorescent light intensity. From such standpoints, the position at which the lymphocytes are present and the position at which the ghosts are present do not overlap and can be satisfactorily discriminated when the maximum allowable noise level is less than or equal to 500 mVp-p, and the white blood cells can be satisfactorily classified as a result. Furthermore, the number of basophils is usually less than or equal to 1% of the entire white blood cells, and thus the fractionation of the basophils may not be performed since it is sufficiently practicable if the white blood cells can be classified into four classifications of neutrophils, lymphocytes, monocytes, and eosinophils. Moreover, the white blood cells may be classified into four classifications, the basophils may be independently measured, and the results may be combined to have five classifications. In this aspect as well, the overlap of the respective regions in which the neutrophils, lymphocytes, monocytes, and eosinophils are present is few, and the white blood cells can be satisfactorily classified into four classifications if the noise level is less than or equal to 500 mVp-p, as shown in  FIG. 19 . Therefore, satisfactory analysis is possible even if the maximum allowable level of the noise contained in the amplified voltage is less than or equal to about 13% (100×500/3906.25=12.8%) with respect to the usage range of the amplified voltage in the analysis of the data processing unit  3 .  
         [0058]     The avalanche photodiode has a property in that the inter-terminal capacity becomes larger and the S/N ratio of the output signal becomes lower as the light receiving surface becomes larger. Therefore, the noise component contained in the side fluorescent light signal increases as the light receiving surface of the avalanche photodiode becomes larger, whereby the high pass cut-off frequency of the low pass filter  84   a  must be set low. In other words, the high pass cut-off frequency corresponding to the maximum allowable level of the same noise changes according to the inter-terminal capacity of the avalanche photodiode.  
         [0059]      FIGS. 22 and 23  are graphs showing the relationship between the inter-terminal capacity of the avalanche photodiode and the high pass cut-off frequency of the low pass filter  84   a  of when the maximum allowable level of the noise is 300 mVp-p and 500 mVp-p, respectively. As a result of the experiment, the high pass cut-off frequency corresponding to the maximum allowable level of the noise of 300 mVp-p when the inter-terminal capacity is 0 pF was 10.28 MHz, as shown in  FIG. 22 . Similarly, when the maximum allowable level of the noise is 300 mVp-p, if the inter-terminal capacity is 1 pF, 3 pF, 5 pF, 10 pF, 18 pF, 36 pF, 56 pF, 120 pF, 240 pF, and 470 pF, the respective high pass cut-off frequency was 10.11 MHz, 9.6 MHz, 9.14 MHz, 7.97 MHz, 6.62 MHz, 5.19 MHz, 4.18 MHz, 2.22 MHz, 1.55 MHz, 1.35 MHz, and 0.87 MHz. The approximate expression of the relationship between the inter-terminal capacity and the limiting frequency of when the maximum allowable level of the noise is 300 mVp-p is as expressed with equation (5). In  FIG. 22 , the curve of equation (5) is shown with a solid line. On the other hand, when the maximum allowable level of the noise is set to 500 mVp-p, if the inter-terminal capacity is 0 pF, 1 pF, 3 pF, 5 pF, 10 pF, 18 pF, 36 pF, 56 pF, 120 pF, 240 pF, and 470 pF, the respective high pass cut-off frequency was 18.86 MHz, 18.62 MHz, 16.94 MHz, 16.35 MHz, 13.47 MHz, 10.48 MHz, 8.09 MHz, 6.32 MHz, 3.46 MHz, 2.47 MHz, 2.18 MHz, and 1.52 MHz, as shown in  FIG. 23 . The approximate expression of the relationship between the inter-terminal capacity and the limiting frequency of when the maximum allowable level of the noise is 500 mVp-p is as expressed with equation (6). In  FIG. 23 , the curve of equation (6) is shown with a solid line.
   Y= 17.289EXP(−0.022 C )+2  (eq.6) 
         [0060]     C: inter-terminal capacity of-avalanche photodiode  
         [0061]     Therefore, the high pass cut-off frequency is set to lower than or equal to the frequency Y provided by equation (5) and the noise level contained in the signal after the noise reduction by the low pass filter  84   a  is set to less than or equal to 300 mVp-p in the present embodiment, but are not limited thereto, and the high pass cut-off frequency may be set to less than or equal to the frequency Y provided by equation (6), and the noise level to lower than or equal to 500 mVp-p, in which case, a satisfactory analysis result is also obtained. In particular, when classifying the white blood cells into four classifications, sufficient precision of analysis can be obtained even if the noise level is set to lower than or equal to 500 mVp-p.  
         [0062]     As described above, the noise contained in the output signal can be further reduced by having a smaller inter-terminal capacity of the avalanche photodiode  58 . The S/N ratio is enhanced by enhancing the intensity of the light emitted from the semiconductor laser light source  52 , but such effect is low compared to when the light receiving surface (i.e., inter-terminal capacity) of the avalanche photodiode  58  is made small, and is also not preferable in terms of power consumption since the energy consumption increases when the level of the output light is increased. It is essential to have the light receiving surface of the avalanche photodiode  58  as small as possible. On the other hand, the light receiving surface may become smaller than the image of the particles projected onto the light receiving surface of the avalanche photodiode  58  by the side light collective lens  55  if the light receiving surface of the avalanche photodiode  58  is made small in excess, and the side fluorescent light signal accurately reflecting the information related to the particles may not be obtained. The image of the particles may be made smaller than the light receiving surface by reducing the magnification of the side light collective lens  55 . However, if the light receiving surface is too small, the positional adjustment with the optical axis becomes difficult and high precision in assembly becomes necessary, which leads to increase in the manufacturing cost. Thus, the avalanche photodiode  58  having a circular light receiving surface of a diameter of 1.5 mm is used in the present invention taking into consideration the noise level of the output signal of the avalanche photodiode, the manufacturing cost of the optical lens, the precision in assembly of the WBC detection unit  5  and the like. The inter-terminal capacity of the avalanche photodiode  58  was 8.4 pF. The high pass cut-off frequency of the low pass filter  84   a  was 2.3 MHz in the present embodiment.  
         [0063]     Although the shape of the light receiving surface of the avalanche photodiode  58  is circular with a diameter of 1.5 mm in the present embodiment, the shape is not limited thereto, and may be a circular shape with a diameter of 0.1 mm-2 mm, may be a square with a side length of 0.1-2 mm, or may be other shapes such as a rectangular shape having a surface area of the same degree.  
         [0064]     Furthermore, the measurement unit  2  and the data processing unit  3  are separately arranged, the blood analyzer  1  is configured by such units in the present embodiment, but configuration of the blood analyzer  1  is not limited thereto, and an integrated blood analyzer having both the function of the measurement unit  2  and the function of the data processing unit  3  may be provided.