Abstract:
A method for performing a dilution step in a blood testing apparatus of a small, defined volume of a blood sample contained in a capillary tube, comprises the steps of providing an adapter for receiving the capillary tube, connecting the adapter to a conduit for diluting liquid, directing a flow of diluting liquid through the conduit and the adapter and at least partly through the capillary tube received therein, and collecting the defined volume of blood sample and the diluting liquid in a vessel. In a blood testing apparatus adapted for performing dilution of a small defined volume of a blood sample contained in a capillary tube, an adapter is inserted in a diluting liquid conduit of the apparatus. The adapter is arranged to receive the capillary tube such that flow of the diluting liquid through the conduit passes at least partly through the capillary tube.

Description:
FIELD OF THE INVENTION 
     The present invention concerns a blood testing method, and more particularly a method for performing a dilution step in a blood testing apparatus. The invention also concerns a blood testing apparatus adapted for performing dilution of a blood sample. 
     BACKGROUND OF THE INVENTION 
     When using a blood testing apparatus, a blood sample is normally taken by venipuncture. The blood is introduced into a small tube containing, for instance, 5 ml. From this tube, blood is sucked into a charging tube of the apparatus. Suction is stopped when the blood reaches a detector indicating that a sufficient amount of blood has been introduced into the apparatus. A well-defined volume of the blood sample, typically 25 μl, is flushed by a defined volume, typically 5 ml, of a diluting liquid into a mixing vessel, where the sample is pre-diluted to typically 1:200. The diluted sample is further diluted 1:200 to a dilution ratio of 1:40000 for counting red blood cells and 1:1 to a dilution ratio of 1:400 for counting white blood cells. 
     When, however, a sample is taken from a finger tip, which is often practised when children are involved, the blood volume is small and is not sufficient for sucking into the apparatus for dilution as described above. Instead, a manual dilution procedure is practiced. The blood sample is manually collected in a small vessel and a defined volume thereof, typically 25 μl, is introduced into a small diameter glass tube, i.e., a capillary tube often referred to as a “microcap ”, or a “mini ” or “micro ” pipette, which sucks the sample by capillary action. The volume contained in the capillary tube is pre-diluted 1:200 by means of a separate dispenser. This pre-diluted sample is then sucked into the apparatus, whereupon final dilution takes place as when a venipuncture test is performed. However, this procedure is circumstantial in that it requires an extra manual step. 
     It would be desirable, thus, to simplify the procedure when making blood tests by way of finger tip puncture, and it is the object of the present invention to provide a method and a device that enable this. 
     SUMMARY OF THE INVENTION 
     According to the present invention, the blood sample is initially introduced, as before, in a capillary tube. The capillary tube is placed in an adapter, which is placed in a conduit from a source of diluting liquid to a mixing vessel where the sample is directly pre-diluted, typically 1:200. The manual pre-dilution step is, thus, superfluous. The capillary tube may remain within the adapter until another capillary tube having a new sample is inserted, since the used capillary tube may be regarded as just an empty glass tube. 
     More specifically, the method of the present invention for performing a diluting step in a blood testing apparatus of a small, defined volume of a blood sample contained in a capillary tube comprises the steps of providing an adapter for receiving the capillary tube; connecting the adapter to a conduit for diluting liquid; directing a flow of diluting liquid through the conduit and the adapter and at least partly through the capillary tube received therein; and collecting the defined volume of blood sample and the diluting liquid in a vessel. 
     In a blood testing apparatus according to the present invention adapted for diluting a small defined volume of a blood sample contained in a capillary tube, the apparatus including a diluting liquid conduit, an adapter is inserted in the diluting liquid conduit, the adapter being arranged to receive the capillary tube such that flow of diluting liquid through the diluting liquid conduit passes at least partly through the capillary tube. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described, reference being made to the accompanying drawings, wherein: 
     FIG. 1 is a schematic cross section through a prior art blood testing apparatus; 
     FIG. 2 is a corresponding representation of an improved blood testing apparatus according to the present invention having an adapter inserted in a conduit of the apparatus; 
     FIG. 3 is a representation corresponding to that of FIG. 2, but showing an adapter inserted in a conduit of the apparatus at a more preferred location; 
     FIGS. 4 a  and  b  is a schematic cross section through an adapter in an disassembled state; and 
     FIG. 5 is a corresponding section through the adapter of FIG. 4 in an assembled, operative state. 
    
    
     DETAILED DESCRIPTION 
     For facilitated understanding of the present invention, reference is made first to the typical prior art arrangement shown in FIG. 1, wherein  11  is a turning valve having a rotatable valve body  12 ,  13  is a mixing vessel and  14  a syringe including a cylinder  15  and a piston  16  axially movable within the cylinder. 
     The rotatable valve body  12  has a through channel  17  and is positionable in at least two different positions. In a first position (shown in FIG.  1 ), a first end of the through channel  17  communicates with a conduit  18 , which is a suction or charging conduit, and a second end of the through channel communicates with a conduit  19  having a valve  20  therein and leading to a non-shown suction device, such as a syringe. In a second position of the valve body  12 , the first end  17   a  of the through channel  17  communicates with a conduit  21  leading to the syringe  14 , and the second end  17   b  communicates with a conduit  22  leading to the mixing vessel  13 . The syringe  14  has in its end a valve  23 , which selectively may put the cylinder  15  in communication with the conduit  21  and a conduit  24  leading to a non-shown source of diluting liquid. 
     The function of the prior art device when making a venipuncture blood test is as follows: The valve body  12  is positioned in the position shown in FIG. 1, and a blood sample is caused to be sucked into the conduit  18 , the through channel  17  and the conduit  19  by means of the non-shown sucking device. As soon as the sample reaches a detector  25  located in the conduit  19 , the valve  20  is shut and the suction stopped. Now, the through channel contains an accurately defined volume of blood sample, typically 25 μl. Upon rotation of the valve body  12  so as to place its ends, and, consequently, the defined volume of blood sample in connection with the conduits  21  and  22 , the piston  16  is displaced so as to in turn displace a defined volume (typically 5 ml) of diluting liquid contained within the cylinder  15  through the conduit  21 , the through channel  17  and the conduit  22  into the mixing vessel  13 , thereby bringing along the defined volume of blood sample contained within the through channel  17  to be mixed with and diluted by the diluting liquid in the mixing vessel. 
     As initially discussed, when taking a fingertip blood sample, the volume is not sufficient to be sucked into the through channel  17 . Instead, a manual pre-dilution takes place outside the apparatus, and the pre-diluted sample is introduced into the mixing vessel  13  through a conduit  26 , and then this sample is further diluted by the volume of diluting liquid contained in the cylinder  15 . 
     In order to avoid the manual dilution step, which is time consuming and may cause contamination of the sample as well as involve a risk of transmission of infection, the present invention proposes insertion of an adapter into a flow path of diluting liquid, said adapter including means for receiving a capillary tube or the like blood sample collector. 
     FIG. 2 shows one location of an adapter  27  between portions  22   a ,  22   b  of the conduit  22 , and FIG. 3 shows another preferred location thereof between portions  26   a ,  26   b  of the conduit  26 . 
     FIG. 4 shows an embodiment of an adapter according to the present invention in a disassembled state. The adapter  27  includes a stationary part  28  and a movable part  29 . 
     The stationary part comprises a block-shaped body  30  having opposite faces  31  and  32 , at least the face  32  preferably being flat. Inlet means and outlet means adapted to be connected to the conduit  26  (FIG. 2) or the conduit  22  (FIG.  3 ), e.g. in the shape of pipe sockets  33 ,  34 , respectively, are arranged at the face  31 . 
     The inlet socket  33  communicates with a bore  35  extending through the body  30  to open at its face  32 . Coaxially to the bore  35  a stepped recess  36  is formed in the face  32 . The recess has a relatively narrow and deep portion  37  and a relatively wide and shallow portion  38 . 
     Also the outlet socket  34  communicates with a bore  39  extending through the body  30  to open at its face  32 . Starting from the face  32 , the bore  39  has a deep widened portion  40  and a relatively shallow, further widened portion  41 . 
     Centrally between the bores  35  and  39  there is provided in the face  31  a relatively wide aperture  42 . A bore  43  extends from the bottom of the aperture  42  to open centrally in the face  32 . Centrally in the aperture  42  are mounted two contact tongues  44 ,  45  having terminal ends  46 ,  47 , respectively, projecting outside the face  31  and spaced contact edges  48 ,  49 , respectively, located in the bottom region of the aperture  42  at substantially equal distances from the axis of the bore  43 . The axes of the bores  35 ,  43  and  39  are parallel, perpendicular to the face  32  and located in a common plane. 
     The movable part  29  of the adapter is likewise constituted by a block-shaped body  50  having a flat face  51 . A central pin  52  extends perpendicularly from the face  51 . It has a diameter corresponding to that of the bore  43  and a length somewhat exceeding the distance between the face  32  and the contact edges  48 ,  49 . At least an outer portion of the pin  52  is electrically conductive. 
     Within the block  50  there is provided an internal channel  53  having mouths  54 ,  55  in the face  51  at locations spaced from the pin  52  distances corresponding to the spacings between on one hand the bore  33  and the bore  43 , and on the other hand the bore  39  and the bore  43 . The axis of the pin  52  and the axes of the mouths  54  and  55  are parallel, perpendicular to the face  51  and located in a common plane. 
     In the region of the mouth  54  the channel  53  has a widened portion in which is inserted a connection tube  56  having a diameter corresponding to that of the portion  37  of the recess  36  and an extension outside the face  51  corresponding to the depth of the recess  36 . A sealing ring  57  having an outer diameter corresponding to that of the wider portion  38  of the recess  36  is arranged around the tube  56 . 
     Correspondingly, in the region of the mouth  55  the channel  53  has a widened portion in which is inserted a relatively long connection tube  58  having a diameter corresponding to that of the portion  40  of the recess  36  and an extension outside the face  51  somewhat less than the depth of the deep recess portion  40 . A sealing ring  59  having an outer diameter corresponding to that of the portion  41  of the bore  39  is arranged around the tube  58 . 
     The connection tube  58  is adapted to internally receive a capillary tube  60  having open ends, thereby to serve also as a protective sheathing for the capillary tube. According to the present invention, it be preferred that the inner diameter of the connection tube is larger than the outer diameter of the capillary tube as shown by the part section of the wall of the connection tube in FIG.  4 . The capillary tube is introduced into the connection tube either from the free end thereof or through a longitudinal slot in the side wall thereof substantially corresponding to the section shown in FIG.  4 . The capillary tube is in no way kept centrally within the connection tube, but is allowed to move freely within the confines of its inner wall. Lengthwise, the capillary tube is kept against movement towards the internal channel  53  by any suitable abutment means or by the cross section of this channel being smaller than the cross section of the capillary tube. 
     After a capillary tube charged with a blood sample has been introduced into the connection tube  58 , the moveable adapter part  29  is assembled with the stationary part  28  by inserting the connecting tube  58  with the capillary tube  60  into the bore portion  40 , the pin  52  into the bore  43  and the connection tube  56  into the portion  37  of the bore  35 , such that the sealing rings  57 ,  59  seal against the respective recess portion  38 ,  41 . In this position, shown in FIG. 5, lengthwise movement of the capillary tube towards, or into, the bore  39  is restricted by any suitable abutment means or by the cross section of the bore  39  being smaller than the cross section of the capillary tube. The adapter is now prepared for a dilution step, in which a diluting liquid is introduced through the inlet pipe socket  33  and further guided through the bore  35 , the connection tube  56  and the channel  53  to the connection tube  58 . There, the diluting liquid is free to flow around the capillary tube as well as through it, thereby displacing the blood sample contained therein out off the capillary tube to mix with the diluting liquid in the mixing vessel  13 . 
     The dilution step is advantageously initiated by an electrically conductive forward end of the pin  52  contacting both contact edges  48 ,  49  of the contact tongues  44 ,  45  whose terminal ends  46 ,  47  are connected by suitable wiring to control means of the blood testing apparatus (not shown). 
     In the embodiment of FIG. 2, to perform a pre-dilution step, a first volume of diluting liquid is forced by the piston  16  through the conduit  21 , the through channel  17  and the conduit part  22   a , through the adapter  27  and the conduit part  22   b  into the mixing vessel  13 . Thereafter, the valve  23  is shifted so as to allow re-charging the syringe with a further volume of diluting liquid. 
     In the preferred embodiment of FIG. 3, where the adapter  27  is inserted in the conduit  26  between two parts  26   a ,  26   b  thereof, on end of a diluting liquid conduit  61  is connected to the conduit  26   b , whereas its other end is connected to a T-valve  62  in the conduit  21 . There is also a valve  63  separating the open end of the conduit  26  (which is used for introduction of a manually diluted blood sample) from the conduit part  26   b . In the pre-dilution step, the diluting liquid is forced by the piston  16  through the valve  62  into the conduit  61 , through the conduit part  26   b , the adapter  27  and the capillary tube into the mixing vessel  13 . The final diluting step is then performed with the valve body  12  in the position shown in FIG.  3  and the valve  62  shifted so as to direct diluting liquid from the syringe  14  through the conduit  21 , the through channel  17  and the channel  22  into the mixing vessel  13  to mix there with the pre-diluted blood sample. 
     Due to the difference in cross sections of the connection tube  58  (inner diameter) and the capillary tube  60  (outer diameter), there is no need to remove the capillary tube after a dilution step has been performed (unless a further capillary tube dilution is to be performed), since there is sufficient cross section left to allow flow in any direction past the capillary tube. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.