Abstract:
A method for fractionated distribution of a blood sample, includes the steps of: 
     a) drawing up a blood sample into a needle; 
     b) distributing via the needle an aliquot corresponding to a specific fraction of the blood sample drawn up, into a flow of a reagent, to thereby produce a mixture of the aliquot and of the reagent; 
     c) collecting the mixture in a mixing and/or measuring receptacle; and 
     d) repeating steps b) and c) at least once to distribute a further aliquot corresponding to a further specific fraction of the blood sample, into a further flow of reagent.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to the field of haematological analysis, and more specifically to the fractionated distribution of a blood sample. 
     The expression “blood sample” in this case denotes a volume of blood obtained from a blood sample taken from a patient, and contained in an analysis container, which for example can be an open tube, or a tube closed by a stopper. In general the blood in question is whole or full blood, taken with an anticoagulant. 
     In haematological analysis, it is often necessary to obtain several fractions of the blood of a patient, which are still known as “aliquots”, and are destined to be diluted with different reagents in order to obtain different analysis results. 
     This is the case in particular for globule counters, which count and differentiate white globules. 
     For practical reasons, it is preferable to take only a single sample of the patient&#39;s blood in a tube, then to fractionate this sample into different aliquots, each of which will then be added to a suitable reagent. 
     For this purpose, fractionating of the blood sample by means of a sample valve is known, according to the teaching, for example, of publication FR 2 622 692 in the name of the applicant. 
     These sampling valves have the advantage that they operate at high speeds, which makes them particularly advantageous for specific types of analysers. 
     However, their main disadvantages are that they require volumes of blood which are far greater than the theoretical volumes necessary for the analysis, they have a complex and costly structure, and they additionally need frequent cleaning, which is difficult to carry out. 
     In the field of biochemistry, it is also known to collect all of a blood serum in a needle, and then to discharge various successive volumes of this sample, for the purpose of different dilutions. 
     This specific technique is used for a blood serum, in other words blood from which the globules have been removed, and which thus has lower viscosity than whole or full blood. 
     SUMMARY OF THE INVENTION 
     The object of the invention is in particular to eliminate the aforementioned disadvantages, and to permit fractionated distribution of a blood sample, in highly efficient conditions. 
     In particular, an object of the invention is to provide fractionated distribution, using means which are simple, reliable, and easy to maintain. 
     A further object of the invention is to permit distribution of this type on the basis of a minimal blood sample volume, without any risk of contamination of the reagents with one another, and in each case ensuring that an aliquot of blood is well mixed with the reagent concerned. 
     For this purpose, the invention provides a method for fractionated distribution of a blood sample, comprising the following operations: 
     a) drawing up a blood sample into a needle; 
     b) distributing via the needle an aliquot of blood, corresponding to a specific fraction of the sample drawn up, into a flow of a reagent, in order to produce a mixture of the aliquot and the reagent; 
     c) collecting the mixture in a mixing and/or measuring receptacle; and 
     d) repeating operations b) and c) at least once on another aliquot of the same sample, and another flow of reagent. 
     Thus, the method according to the invention makes it possible to fractionate a blood sample contained in a needle, into at least two aliquots which are each mixed by dilution with an appropriate reagent, in each case in a mixing and/or measuring receptacle. 
     As a result, each aliquot, which corresponds to a specific fraction of the sample, is forced into the flow of reagent, thus permitting thorough mixing of the blood and reagent to be analysed. 
     The aliquots have selected volumes which can be identical or different, thus providing the method according to the invention with considerable flexibility of use. 
     The above-described operation a) advantageously comprises drawing up the blood sample into the needle which already contains a fluid, a bubble of gas, for example of air, being formed on the interface between the fluid and the blood sample. 
     By this means, there is no risk of mixing taking place between the blood sample and the fluid, since the latter simply acts as an intermediary for drawing up the sample, and then for gradual ejection of this sample in various aliquots, according to the analyses to be carried out. 
     According to another characteristic of the invention, the blood sample is drawn up into the needle from a tube of an open or closed type, containing a volume of blood to be analysed. 
     The blood sample which is drawn up into the needle advantageously has a volume which is greater than the sum of the respective volumes of the aliquots to be distributed, such as to provide an optional excess of volume, in order to obtain an initial volume of blood in the needle on completion of the operation a), and/or a residual volume of blood in the needle on completion of the operation d), thus making it possible to keep the aliquots intact. 
     The initial volume of blood can be discharged before the fractionated distribution takes place. 
     The residual volume of blood alone is affected if there is residual fluid present before sampling of the blood takes place. This residual volume can be discharged after the distribution, for example into a rinsing vessel, which allows the needle to be used to collect a further blood sample. 
     According to a further characteristic of the invention, the operation b) comprises injection of the aliquot of blood and injection of the flow of reagent under controlled conditions, and substantially simultaneously. 
     According to a preferred embodiment of the invention, this operation b) comprises in succession: 
     b1) injection of an initial part only of the flow of reagent; 
     b2) simultaneous injection of the aliquot of blood and of an intermediate part of the flow of reagent; and 
     b3) injection of a final part only of the flow of reagent. 
     According to a further characteristic of the invention, in operation b), the flow of reagent is injected such that this flow reaches the end of the needle by means of which the aliquot of blood is injected. 
     The aliquot of blood is preferably injected in a substantially vertical descending direction, whereas the flow of reagent is injected in a direction which is horizontal or inclined relative to the horizontal, such as to assist rotary motion or eddying, thus permitting thorough mixing of the blood and the reagent. 
     The method according to the invention can comprise at least one additional operation, consisting of depositing an aliquot of blood in a fluid medium or on a solid support, for example on a glass plate. 
     This makes it possible to combine operations of mixing aliquots and reagents, with operations of a different kind. 
     According to another aspect, the invention relates to a device for implementation of the above-described method, comprising: 
     a needle which can draw up a blood sample; 
     a first volumetric distributor, which is connected to the needle, in order to draw up and eject selected volumes of blood; 
     at least one reagent injection nozzle, which can be disposed in the vicinity of the end of the needle; 
     a second volumetric distributor, which is connected to the nozzle, in order to eject selected volumes of a flow of reagent; 
     a control unit which is connected to the first volumetric distributor and to the second volumetric distributor (s), in order to actuate the latter in a coordinated manner; and 
     at least one mixing and/or measuring receptacle, in order to collect the mixture formed from the blood and the reagent, which are distributed respectively by the needle and the injection nozzle. 
     The injection nozzle is preferably oriented towards the open end of the needle, via which the blood is ejected. 
     The needle is advantageously substantially vertical, with its open end facing downwards, whereas the injection nozzle extends in a direction which is horizontal or inclined relative to the horizontal. 
     The injection nozzle is advantageously integral with a mixing and/or measuring receptacle. 
     This receptacle can be a vessel which is delimited by a peripheral wall, the injection nozzle opening into the vessel in the vicinity of the peripheral wall. 
     According to a variant embodiment, the receptacle is a T-shaped connection with a first, a second and a third branch, wherein the free end of the needle opens into the first branch, the second branch acts as an injection nozzle for the reagent, and the third branch constitutes an outlet for the mixture. 
     According to a preferred embodiment of the invention, the device comprises motor means, which can displace the needle, and bring it in succession towards the receptacles, under the control of the control unit. 
     It will be appreciated that the needle can be fixed, and the receptacles can be brought in succession close to the needle. 
     The first volumetric distributor and the second volumetric distributor(s) each advantageously comprise at least one syringe piloted by a motor, which is for example of the step type. 
     The following description, which is provided by way of example, refers to the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows schematically a distribution device according to the invention, of which, for the sake of simplification, a single mixing and/or measuring vessel is shown; 
     FIG. 2 is a detail of FIG. 1, showing the vessel, the needle and the injection nozzle; 
     FIG. 3 is a view in transverse cross-section along line III—III in FIG. 2; 
     FIG. 4 is a schematic representation of a device according to the invention, comprising a rinsing vessel and three mixing and/or measuring vessels; 
     FIG. 5 shows schematically the content of a needle containing a blood sample, before the latter is distributed and fractionated; 
     FIG. 6 is a schematic representation of a needle associated with a known cleaning device according to publication FR 2 707 760; and 
     FIG. 7 is a view in longitudinal cross-section of a receptacle in the form of a T-shaped connection, this connection accommodating a sampling needle and an injection nozzle. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The device in FIG. 1 comprises a needle  1 , which can contain a blood sample E, this needle extending in a substantially vertical direction and having a lower end  2  which is open, and an upper end  3  which is connected by means of a duct  4  to a first volumetric distributor  5 , consisting of a syringe  6  actuated by a step motor  7 . A control unit  8  comprising a microprocessor  9  is provided in order to pilot the step motor  7 , and thus allow the needle to draw up the blood sample E, and then to eject the fractions or aliquots of this sample under controlled conditions, as will be described hereinafter. 
     A fluid L which fills the syringe  6 , the duct  4  and partially the needle  1 , acts as an intermediary in order to control the steps of drawing up into, and ejection from the needle  1 . 
     The control unit  8  can also displace the needle  1  by suitable motor means (not shown). 
     In the position in FIG. 1, the needle  1  is in the vicinity of an injection nozzle  10 , which can convey a flow F of a reagent R in the direction of the open lower end  2  of the needle, in order to permit thorough mixing of an aliquot of blood A (ejected by the needle  1 ), and of the flow F of the reagent R. 
     The nozzle  10  is connected by means of a duct  11  to a second-volumetric distributor  12 , comprising a syringe  13  activated by a step motor  14 , which is also controlled by the control unit  8 . 
     The injection nozzle  10  is supported by a mixing and/or measuring receptacle, in this case consisting of a vessel  15 , which can receive the mixture formed from the aliquot of blood A and the flow F of reagent R. 
     As can be seen more particularly in FIGS. 2 and 3, the vessel  15  is delimited mainly by a peripheral wall  16 , which has a generally cylindrical shape and a vertical axis. This wall  16  has an open upper part  17 , and is extended in its lower part by a frusto-conical wall  18 , which leads to an outlet duct  19  for discharge of the mixture M. 
     The injection nozzle  10  has an axis XX (FIG. 2) which is slightly inclined relative to the horizontal, and intersects the axis YY of the needle  1 . The latter is disposed in the vicinity of the wall  16  of the vessel  15 , such that the aliquot of blood A is forced by the flow F of reagent to a point close to the wall  16 , thus assisting thorough mixing of the blood and the reagent by means of a rotary motion which creates a type of eddy. The mixture M thus created is then measured and/or ejected through the outlet duct  19  of the vessel  15 . 
     FIG. 4 shows schematically a device which is similar to that in FIG. 1, and comprises three mixing and/or analysis vessels  15 - 1 ,  15 - 2  and  15 - 3 , which are similar to the vessel  15  previously described, and support respectively three injection nozzles  10 - 1 ,  10 - 2  and  10 - 3 , which are similar to the injection nozzle  10  previously described. 
     These injection nozzles are connected respectively to three volumetric distributors  12 - 1 ,  12 - 2  and  12 - 3  (shown schematically), which are similar to the volumetric distributor  12  previously described. 
     On each occasion, the distributors  12 - 1 ,  12 - 2  and  12 - 3  can convey a specific volume of reagent into the corresponding vessel. The volumetric distributors  12 - 1 .  12 - 2  and  12 - 3  are piloted by the control unit  8 . 
     In the embodiment in FIG. 4, the device additionally comprises a rinsing vessel  20 , with which there is associated an injection nozzle  21 , which is connected to a volumetric distributor  22 , in order to permit distribution of a rinsing fluid. The volumetric distributor  22  is also piloted by the control unit  8 . 
     The latter also pilots motor means  23 , which can displace the needle  1 , and bring it in succession towards the rinsing vessel  20  and the vessels  15 - 1 ,  15 - 2  and  15 - 3 , according to a sequence of operations programmed by the microprocessor  9 . 
     Thus, the needle  1  can be introduced into an analysis tube  24  which contains the blood S of a patient, this tube being in the form of an open tube in the present case. 
     The motor means  23  can displace the needle in vertical or horizontal translation, as shown by the double arrows. 
     The functioning of the device in FIG. 4 is now described, by way of example. 
     The needle  1  is displaced by the motor means  23 , under the control of the control unit  8 , such as to penetrate in the interior of the analysis tube  24 . The volumetric distributor  5  is then actuated by the control unit  8 , in order to draw up a specific volume of blood, which constitutes a sample E. This sample E is contained in the needle  1 , and is separated from the fluid L by an air bubble A (FIG. 5) which forms an interface, and thus prevents mixing between the blood and the fluid. The latter acts as an intermediary in order to control the drawing up into the needle  1 , and ejection from it. 
     The needle is then withdrawn from the tube  24 , and subsequently moved such that it is positioned opposite the rinsing vessel  20 , and is inserted in the latter. The volumetric distributor  5  is activated by the control unit  8 , in order to eject an initial volume VI (see FIG.  5 ). This initial volume is received in the rinsing vessel, and is discharged by means of a flow of rinsing fluid L conveyed by the nozzle  21 , under the action of the volumetric distributor  22  which is piloted by the control unit  8 . The needle  1  is then extracted from the rinsing vessel  20 , moved opposite the mixing and/or analysis vessel  15 - 1 , and inserted in the latter, such that the end of the needle is positioned opposite the injection nozzle  10 - 1 . The volumetric distributor  12 - 1  is then actuated by the control unit  8 , in order to eject a fraction of the sample E, which corresponds to a first aliquot A 1  (FIG.  5 ). This aliquot A 1  is mixed with a flow of a first reagent R 1  in order to produce a mixture, which is measured and/or collected at the outlet of the vessel  15 - 1 . 
     The needle  1  is then extracted from the vessel  15 - 1 , and is subsequently brought towards the vessels  15 - 2 ,  15 - 3 , into which the aliquots A 2  and A 3  respectively (FIG. 5) are ejected. These aliquots are mixed with flows of reagent R 2  and R 3 , in order to produce mixtures which are measured and/or collected at the outlet of the vessels  15 - 2  and  15 - 3 . 
     After these operations, there remains in the needle a residual volume VR of blood (FIG.  5 ), which is still separated from the fluid L by the air bubble A. This residual volume VR must be discharged. 
     For this purpose, the needle  1  is displaced once more towards the rinsing vessel  20 , and the residual volume VR is discharged by a flow of the rinsing fluid, which at the same time ensures that the lower end  2  of the needle  1  is cleaned, so that similar operations can be carried out on another sample. 
     The control unit  8  makes it possible to pilot the sequence of operations, such that drawing up of the blood sample, then distribution of the sample in aliquots obtained from fractionating of the sample, are carried out under very accurate controlled conditions. 
     The various volumetric distributors are each actuated by step motors, which consequently make it possible to collect by drawing up, or to distribute by ejection, very accurate volumes of blood, reagent or rinsing fluid, with flow rates which are likewise accurate. 
     In order to ensure that an aliquot of blood and a flow of reagent are mixed thoroughly in a mixing vessel, it is advantageous to carry out firstly injection of only an initial part of the flow of reagent, then simultaneous injection of the aliquot of blood and of an intermediate part of the flow of reagent, and to end by injection of only a final part of the flow of reagent. 
     By way of example, the initial, intermediate and final parts of the reagent can correspond respectively to approximately 10%, 80% and 10% of the total volume of the flow of reagent. 
     It will be appreciated that the above-described operating sequences can be subjected to many variants. 
     In particular, two successive mixing operations can be carried out in a single vessel, and a rinsing operation can be interposed between two mixing operations which involve different reagents etc. 
     In general, the mixing operations are carried out starting with the least pollutant or contaminating reagent, and ending with the most pollutant or contaminating reagent. 
     In the case in FIG. 6, the needle  1  is associated with a cleaning device  25  of the type described in publication FR 2 707 760 in the name of the applicant. This cleaning device substantially comprises a guiding unit  26 , which contains an emptying duct  27  and a rinsing duct  28 . In addition, the device  25  comprises a pre-piercing needle  29 , which has a bevelled end  30  which can pierce the stopper (not shown) of an analysis tube. 
     In the embodiment in FIG. 7, to which reference is now made, the mixing and/or measuring receptacle no longer consists of a vessel, but of a T-shaped connection  31 , which has a first, vertical branch  32  in which the needle  1  can be introduced, a second, horizontal branch  33 , in which the reagent is injected, and a third branch  34 , which is opposite the branch  33 , and acts as an outlet for the mixture. The branch  33  is disposed such that the flow of reagent reaches the open end  2  of the needle. 
     It will be appreciated that the invention is not limited to the embodiments previously described, and can be subjected to many variants. 
     The method and the device according to the invention provide considerable flexibility of use, particularly concerning the number and volume of the aliquots of blood to be processed.