Abstract:
A portable hand-held blood sampling device having a self-filling capability includes a blood separation filter. The filter has a plurality of pores sized to permit passage of selected blood constituents such as blood plasma through the device. The device has a separated blood conduit that extends beyond the outlet of the device and is shaped for easy penetration into a self-sealing septum of a blood analyzer. An annular shield extends from the device outlet beyond the conduit to prevent inadvertent contact of the conduit by a user.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to portable hand-held devices for extracted blood elements, such as blood plasma, from whole blood.  
         BACKGROUND OF THE INVENTION  
         [0002]    The use of blood sampling devices is known in the art. Typically, blood samples are taken from a patient utilizing a finger stick or draw tube. As is recognized in the art, the obtained sample is difficult to analyze. For example, the sample contains a variable proportion of cells which affect the quantization of analytes measured in non-equilibrium assays. The blood sample is subject to clotting with the end result of clogging the small channels in typical blood analyzers. The blood sample contains fragile blood cells that, if ruptured, can alter the concentration of some analytes. Moreover, a very high number of blood cells could overwhelm the read capability of an analyzer that is cytometer-based. Some sampling devices known in the art, such as, for example, described in U.S. Pat. No. 5,919,356, utilize a needle that is insertable into a patient to draw blood, by pulling a plunger of a syringe, which then flows into a chamber that contains membrane fibers. Filtration through the membrane is accomplished by either shaking the device or by depressing the plunger of the syringe. The separated sample is contained in a collector chamber. Devices of this type are not intended for use with a blood analyzer. Moreover, the devices of the prior art, such as described above, require puncturing the skin of a patient by way of a needle/syringe arrangement to extract an unnecessarily large volume of blood from the patient. This presents a potential trauma affect on patients sensitive to needle punctures of their skin. The present invention serves to remedy the shortcomings of the prior art.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention is directed to a device for collecting a blood sample that is to be analyzed by the use of a blood analyzer. The device comprises a hollow fluid tight tube having an inlet opening for receiving a blood sample and a separation filter in the tube that serves to separate out desired blood constituents for later analysis. Such a constituent is blood plasma and the filter is hollow and contains a plurality of pores sized to prevent whole blood and blood cells from passage into the hollow part of the filter while providing passage of blood plasma through the filter. The tube has a wettable surface and the relative size of the filter within the tube provides for self-filling capability of the device through capillary action, thus providing self-filling capability combined with a blood separation filter in one device. The device includes a conduit that extends from the filter to the outlet of the device. The conduit is a stent-like structure that has a tapered end for easy penetration into a septum of an analyzer that acts as a self-closing sample inlet channel in the analyzer manifold. Annularly disposed about the outlet of the device is a shield that extends away from the outlet a distance greater than the separated blood conduit. The shield protects the conduit from inadvertent contact by the user of the device. This protects the sample from any contamination by a user and prevents the user from contact with a contaminated sample.  
           [0004]    In practice, a droplet of blood is introduced at the device inlet and by virtue of the combined affects of the wettable interior surface of the tube and the interior fill volume, blood is drawn into the device under capillary action into the device. The device is placed on an analyzer such that the separated blood conduit pierces the inlet channel septum whereupon a vacuum is drawn by the analyzer to draw the blood sample through separation filter thereby introducing the separated blood, i.e., blood plasma, into the analyzer.  
           [0005]    As an alternate embodiment of the present invention, the inlet of the device may be formed with a sharp projection to act as a blood drawing lancet and the shield may be in the form of an anchoring device, such as a Luer Lock. As a result of the aforementioned features, the present invention is characterized as being a point of need clinical analyzer; that is compact and portable; that provides a small volume of plasma in a relatively short period of time; that is relatively inexpensive compared to traditional blood draw disposables; that protects the operator from contact with potentially infectious sample; and lastly does not require a dedicated piece of equipment to separate plasma from cells. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a cross-sectional view of an embodiment of the present invention;  
         [0007]    [0007]FIG. 2 is a partial cut-away perspective view of the embodiment of FIG. 1;  
         [0008]    [0008]FIG. 3 is an alternate embodiment of the invention of FIG. 1; and  
         [0009]    [0009]FIG. 4 is a partial cut-away perspective view of the embodiment of FIG. 3.  
     
    
     DETAILED DESCRIPTION  
       [0010]    Referring now to the drawings, there is shown an embodiment of the blood sampling device of the present invention. More specifically, FIGS. 1 and 3 show a device  10  formed of a hollow cylindrical tube  12  having an inlet end  14  and an outlet end  16 . The tube  12  may be manufactured of any one of a number of conventional materials, such as rigid plastic known in the art. The outlet end  16  includes an end cap  18  that is anchored to the tube  12  in fluid tight fashion. The end cap  18  may be anchored to the tube  12  for example, by means of a fluid insoluble adhesive and the like. The end cap  18  has an overlap portion  20  that circumferentially overlaps the outlet  16  and a fluid sealing O-ring  22  is positioned annularly between the tube  12  and the overlap portion  20  in respective recesses so as to provide further fluid sealing at the outlet  16 . Although the cap  18  is shown as part of the device assembly, it is to be understood that the cap  18  may be made integrally as part of the tube  12  and such is within the contemplation of the present invention.  
         [0011]    The end cap  18  includes a relatively small stent-like conduit  24  that extends across the boundary defined by the tube outlet  16  to a station immediately beyond the outlet  16 . The portion  26  of stent  24  beyond the outlet  16 , has a somewhat conical profile to, as will be discussed later, facilitate penetration of the stent  24  into a self-closing sample inlet channel of a blood sample analyzer manifold. An annular shield  27  extends outward from end cap  18  to a station beyond the distal end of the stent conical portion  26 . The shield  27  reduces the potential of inadvertent contact of the stent  24  during handling of the device  10  so as to maintain the stent  24  free of contamination during use and avoid user contact with a contaminated sample.  
         [0012]    The stent portion  28  extends interiorly of the tube  12  a distance sufficient to provide mating engagement with filter  30 . The stent portion  28  includes an outwardly extending annular lobe  32  dimensioned to securely fit within filter annular recess  34  located proximate to the filters distal end  36 . The filter  30  may be anchored to the stent portion  28  by means of a press-fit arrangement or by use of adhesives known in the art. The device inlet  14  defines an inlet chamber  38  and the filter  30  extends essentially the length of the interior of tube  12  from between the end cap  18  into inlet chamber  38 . The filter  30  has a generally tubular shape having a circular cross-section, a closed end  40  and an open end  36  that is, as described above, mounted on stent portion  28  in fluid tight relationship. The filter  30  is formed of a membrane that is naturally impervious to the passage of whole blood and as shown in FIGS. 2 and 4, has a plurality of pores  42  disposed along and around filter wall  44 . The region  46  between the filter  30  and the interior of the tube  12  including the inlet chamber  38  defines a fill volume that holds whole blood that is introduced at the inlet  14 . The pores  42  extend through filter wall  44  and are sized to limit the flow of only blood plasma through the filter walls  44  and into the filter interior  48 . The pore size may be about 2 micrometers in diameter and preferably in the range of about 0.1 to 1.0 micrometers. As will be discussed later, the process of drawing plasma into the filter interior  48  and out of the device  10  through stent  24  is under the aspiration action of an external blood analyzer. The pores  42  lie in a region starting at the filter distal end  36  and progresses toward the closed end  40  a distance that corresponds to about half of the initial blood fill volume. The tube  12  has an interior wall  50  conditioned to have a wettable lumenal surface. The cross-sectional area of the tube  12  is sized such that, in combination with the wettable surface characteristics of the interior wall  50 , the device is self-filling by capillary action. In that regard, the volume of the tube is sized to be in the range of about 0.5 milliliter and the internal diameter of the tube is in the range of about 1 millimeter. Accordingly, when the device is full of blood, the weight associated with the blood is less than about 5 grams. The filter  30  is essentially cylindrical and sized such that the volume immediately surrounding the filter should be entirely sheathed in blood, even if the amount of blood is insufficient to completely fill the tube  12 . To prevent clotting of blood contained within the tube  12 , an anti-coagulant reagent  52 , preferably in dry form, is dispersed throughout the interior of the tube  12 . In such manner, the flow of blood plasma from the tube  12  through the filter  30  is facilitated.  
         [0013]    In practice, use of the device in combination with a blood analyzer is as follows. A droplet of blood is introduced at the device inlet end  14 , an aliquot of blood enters tube  12  under the influence of capillary action. Upon entry into tube  12 , the blood dissolves the anti-coagulant  52  that inhibits the clotting of the blood. Because of the self-filling nature of the device  10 , sample retention within the tube  12  is maintained irrespective of the device orientation. Subsequent to introducing the sample in tube  12 , a device user inserts the end cap  18  into the sampling port of a blood analyzer. The stent portion  26  penetrates a self-closed inlet channel in the analyzer manifold. Typical self-closing techniques and apparatus utilize a pierced septum of a compliant material, such as silicone rubber. Once the device  10  is inserted into the sampling port of the analyzer, the analyzer pump aspirates through sample inlet  14  to develop a negative pressure with respect to ambient. The negative pressure pulls plasma from the blood sample in tube  12 , through the pores  42  and into the filter interior  48  and finally into the analyzer manifold. No additional venting is needed for this operation as the sampling device  10  is vented through inlet  14 . The aspirated sample is preceded by a variable amount of air. The analyzer pump dispenses the first portion of the sample to waste to dispose of this air. Once an adequate sample has been aspirated, the analyzer routes wash fluid around and through stent  24  within the tube  12  to remove droplets of sample that may contaminate the outside of the device inlet  14 . An operator then removes the device  10  which closes the self-closing inlet of the analyzer so that wash fluids may be circulated by the port without concern for leakage or aspiration of air. Importantly, the extended end cap shield  27  helps prevent an operator from contacting stent  24  which may be contaminated with sample.  
         [0014]    Furthermore, when aspirating from the stent  24 , there will be flow resistance as the plasma moves across the filter wall  44  through pores  42 . Flow resistance is higher for plasma than it is for air. If the filter  30  were partially surrounded by blood and partially surrounded by air due to an incomplete fill, the fluidic circuit would be shorted out by the presence of the lower resistance air path. Accordingly, and as shown in FIGS. 2 and 4, the distribution of the pores  42  terminates towards the filter closed end  40  otherwise after separating a small amount of plasma air would contact the filter  30  and short out the plasma flow. Air should not contact the porous region of the filter  30  until all of the desired separated sample is produced. The device  10  produces a separated plasma volume no larger than about half the blood sample volume because the other half of the blood sample is blood cells. The amount of plasma removed from the sample will decrease the fill height and once the fill height is less than the height of the porous region of the filter  30 , there will be no further separation. To obtain the maximum amount of plasma, the porous portion of the filter  30  should terminate at a height that corresponds to no more than the height of half of the initial blood fill volume.  
         [0015]    An alternate embodiment of the present invention is shown in FIGS. 3 and 4. Rather than the flat cut profile as shown in FIG. 1 at the inlet  14 , the device  10  has an angled cut at the inlet  14 ′ with respect to the elongated tube  12  so as to produce a sharp projection  54 . The projection  54  serves as a lancet for piercing a patient&#39;s skin for obtaining a small blood sample. Due to the self-filling nature of device  10 , only a small amount of blood required to fill the device need be drawn from the patient, making the procedure of obtaining blood very fast and efficient.  
         [0016]    Although the present invention has been described in considerable detail with reference to certain preferred versions, many other versions should be apparent to those skilled in the art. Therefore, the spirit and scope of the appended claims should not necessarily be limited to the description of the preferred versions contained herein.