METHOD AND DEVICE FOR SEPARATING SERUM/PLASMA FROM BLOOD

Abstract: Method and device for separating the serum included in a certain volume of blood by way of centrifugation, said volume of blood being introduced into a test tube (1) in which a so-called separating body (5; 5') is also present, after which the test tube (1) is centrifugalized, the blood being separated into a heavy phase (11) containing redblood corpuscles and a light phase (12) containing serum or plasma, the separating body (5; 5') being given such a specific gravity that upon centrifugation it enters a position in the boundary layer between the heavy and the light phase (11 and 12, respectively). What characterizes the invention is that a mass (9; 9') stored in the separating body (5; 5') is moved out of this towards the heavy phase (11) and seals between separating body (5; 5') and test tube (1). When said mass (9; 9') is removed from the separating body (5; 5') a negative pressure will arise therein which is utilized to suck up accumulated leukocytes and trombocytes in the separating body (5; 5').

Description: Method and device for separating serum/plasma from blood This invention relates to a method of separating serum/plasma included in a certain volume of blood, said volume of blood being introduced into a test tube, in which a so-called separating body is also present, after which the test tube is centrifugalized, the blood being separated into a heavy phase containing red blood corpuscles and a light phase containing serum or plas¬ ma, the separating body being given such a specific gravity that upon centrifugation it enters a position in the boundary layer between the heavy and light phase. The invention also relates to a device for se- paration according to the above. A plurality of various technical methods are known to provide separation of a sample of blood enclosed in a test tube to a heavy phase containing red blood corp¬ uscles and a light phase containing serum. A general method is arranging a silicon compound having a specific gravity between that of the heavy phase and the light phase on the bottom of a test tube. Upon centrifugation of the sample the silicon compound will form a barrier between the heavy phase and the light phase so that the light phase, i.e. the serum/- plasma can be removed from the test tube while the heavy phase, i.e. the red blood corpuscles, remains in the test tube. However, this technique does not provide any mechanical barrier between the two phases and, moreover, the accumulation of leukocytes and trσmbo- cytes in the boundary layer between the two phases is not taken charge of, meaning that the serum/plasma will be "contaminated" by these leukocytes and trombσcytes. It is also known in separation of the kind de- scribed above to use a quite mechanical separating body having such a specific gravity that it will adjust it¬ self upon centrifugation of the test tube in the bound¬ ary layer between the heavy and the light phase. The mechanical separating bodies have different types of seals bearing on the walls of the test tube. However, these seals cannot be made too efficient as the separating body must be able to slide within the test tube. Moreover, the accumulation of leukocytes and trombocytes in the boundary layer between the heavy and the light phase is not taken charge of but will "con¬ taminate" the serum/plasma. It is the object of this invention to show a me¬ thod and a device of the kind mentioned above, where the separation is achieved by means of a separating body providing, on one hand, an adequate mechanical sealing between the two phases and, on the other hand, takes charge of the concentration of leukocytes and trombocytes taking place in a separation through cen- trifugation. This object of the invention is realized by a me¬ thod and a device to which have been given the charac¬ teristic features defined in the following claims. According to a preferred embodiment of the inven- tion the separating body is arranged in a test tube open at both ends, said ends being sealed by means of elastic members and, as a result of thi3, vacuum pre¬ vailing in the test tube. An illustrative example of the invention will be described below with reference to the enclosed draw¬ ings, wherein Fi . 1 shows a test tube in which a se¬ parating body according to the invention is placed and the test tube is in a position of sampling; Fig. 2 shows the test tube according to Fig. 1 in a position for separation; Fig. 3 shows the test tube according to Fig. 1 after separation; and Fi . 4 shows an alterna- tive embodiment of the separating body according to the invention. The test tube 1 shown in Figs. 1-3 is open at its two ends. One end (the upper one in Fig. 1) of the test" tube 1 is sealed by means of a plug 2 of an elastic ma¬ terial, said plug 2 being of a type that can be pene¬ trated a plurality of times by a cannula 3 without los¬ ing its sealing ability upon removal of the cannula 3. At the other end of the test tube 1 (the lower one in Fig Λ 1) a relatively thin membrane 4 of an elastic material is arranged which is threaded onto said end of the test tube 1 to provide a sealing closure. There is vacuum in the test tube 1 which has the effect that the membrane 4 will bulge inwards towards the tube 1. A separating body 5 is also placed within the test tube 1. This separating body 5 consists of an outer shell of a shape-permanent material, e.g. rigid plas¬ tic, the material of the shell also having the property not to react with blood. In the illustrative example shown the shell has a cup-shaped recess 6, which is associated with a cylind¬ rical recess 8 by way of a passage 7. A viscous or, as an alternative, fine granular mass 9 having a specific gravity somewhat higher than the specific gravity of the shell is placed within the cylinder-shaped recess 8. The test tube 1 with its associated separating body 5 described above is used as follows. In the starting position shown in Fig. 1 the se¬ parating body 5 is located in connection with the memb¬ rane 4, i.e. at the lower end of the test tube 1. A sample of blood 10 is thereafter supplied to the test tube 1 by way of the cannula 3 in Fig. 1, the blood being sucked into the test tube 1 thanks to the vacuum prevailing therein. When a desired quantity of blood has been supplied to the test tube 1 the cannula 3 is removed, and the plug 2 will close the test tube 1 sealingly at its upper end in Fig. 1. Before separation of the sample of blood through centrifugation of the test tube 1 the test tube is turned upside down so that it enters the position shown i Fig. 2, i.e. the sample 10 is located beneath the se¬ parating body 5. Upon centri ugation the sample of blood will sub- stantially be separated into a heavy phase 11 and a light phase 12, see Fig. 3. The heavy phase consists of red blood corpuscles, erythrocytes , while the light phase consists of serum or plasma. In the range between the heavy and the light phase a layer of leukocytes and trombocytes is accumulated which, thus, have a specific gravity between that of the red blood corpuscles and that of the serum/plasma. When the centri ugation is carried out the se¬ parating body 5 which, thus, consists of the shell and the viscous or fine granular mass, will also seek out a balance position in the test tube corresponding to its specific gravity which is intermediary in relation to the specific gravity of the red blood corpuscles and that of the serum/plasma. By giving the separating body 5 a specific gravity substantially corresponding to that of the leukocytes and the trombocytes the separating body 5 will enter a balance position on a level with the layer of leuko¬ cytes and trombocytes between the heavy and the light phase . When the separating body has entered this balance position the mass 9 placed in the recess 8 will move downwards out of the recess 8 during the continued cen¬ trifugation. Due to a high viscosity and frictional force this will not take place earlier during the cen¬ trifugation . The mass 9 has a somewhat higher specific gravity than the shell of the separating body 5 but a somewhat lower specific gravity than the heavy phase 11 meaning that the mass 9 will flow at least partly around the lower edge of the shell and seal the space between the separating body 5 and the wall of the test tube. In this way the red blood corpuscles have been se¬ parated efficiently from the rest of the sample of blood in the test tube 1. When the mass 9 is moved at least partly downwards out of the recess 8 a negative pressure will arise in the part of said recess 8 facing the passage 7. This has the effect that a great portion of the leukocytes and trombocytes accumulated on a level with the se- parating body 5 will be sucked by way of the cup-shaped recess 6 into the part of the recess 3 where there is negative pressure. This is extremely advantageous as it is desirable that the serum or plasma is freed from leukocytes and trombocytes as much as possible, which are not desired in the following analysis. Thus, when the separation by way of centrifugation is finished subs an ially only serum/plasma is found above the separating body. This serum/plasma which is thus to be analysed is removed from the test tube pre- ferably by means of a cannula penetrating the membrane 4 and sucking out a desired quantity of serum/plasma. In this way a person handling the test tube 1 need not get in contact with its contents which is a great ad¬ vantage i.a. in view of the infection risks. In the embodiment of a separating body 5' accord¬ ing to the invention shown in Fig. 4 this has a conical primary form and the recess 8' has also been given such a form. In this illustrative example the cup-shaped re¬ cess 6' is directly connected with the recess by way of ' an aperture 7' . At its lower end the recess 8' has a relatively small outlet opening for the mass 9' meaning that a mass of a somewhat lower viscosity than in the illu¬ strative example described above can be used in this illustrative example. To sum up, it can thus be established that the se¬ parating body of this invention provides a mechanical barrier between the separated phases through the seal¬ ing effect of the mass 9 against the wall of the test tube and that the accumulation of leukocytes and trom- bocytes is sucked into the recess 8 in the separating body 5 at least partly. In the illustrative example described the separat¬ ing body according to the invention is placed in a test tube which is open at both its ends and sealed there by elastic members. Vacuum prevails within the test tube. This arrangement has several advantages as has been stated above. However, it is also possible to use the separating body of the invention at other types of test tubes, but handling thereof, will ' be somewhat more aw- kward. Of course the dimensions of the separating body must be adapted to the type of test tube used. As far as the play between the wall of the test tube and the outer periphery of the separating body is concerned a suitable size of this appears to be about 0.5 mm. Of course this is only an indication for the sake of exemplification. The illustrative examples of separating bodies given above are by no means complete but further embo- diments within the scope of the invention are possible, the spherical form being especially worth mentioning. The invention can also be freely varied in other respects within the scope of the following claims.

Claims: PATENT CLAIMS 1. A method of separating serum/plasma included in a certain volume of blood, said volume of blood being introduced into a test tube (1) in which a so-called separating body (5; 5') is also present, after which the test tube (1) is centrifugalized, the blood being separated into a heavy phase (11) containing red blood corpuscles and a light phase (12) containing serum/- plasma,, the separating body (5; 5') being given such a specific gravity that upon centrifugation it enters a position in the boundary layer between the heavy and the light phase (11 and 12, respectively) , c h a ¬ a c t e r i z e d in that a certain quantity of a mass (9; 9') having a somewhat higher specific gravity than the rest of the separating body (5; 5') and stored in the separating body (5; 5') is moved out of the se¬ parating body (5; 5') towards the heavy phase (11) dur¬ ing a later part of the centrifugation and seals the space between the portion of the separating body (5; 5') closest to the heavy phase (11 and the test tube (1), a negative pressure being formed within the se¬ parating body (5; 5') in connection with said motion of the mass (9; 9'), with the result that at least part of leukocytes and trombocytes accumulated in the boundary layer between the heavy phase (11) and the light phase (12) is sucked into the separating body (5; 5') through a cannula (7) , aperture (7') or the like turned in the direction of the light phase (12) . 2. A device for providing separation of serum/- plas a contained in a certain volume of blood upon centrifugation in a test tube (1) , said device consist¬ ing of a separating body (5; 5') placed in the test tube and having a specific gravity between the specific gravity of a heavy phase (11) containing red blood cor¬ puscles and a light phase (12) containing serum/plasma, c h a r a c t e r i z e d in that the separating body (5; 5') has an outer contour at least in one portion that corresponds to the inner contour of the test tube (1), the transversal measure of the separating body (5; 5 ' ) in said portion being somewhat smaller than the inner transversal measure of the test tube (1), and that said separating body (5; 5') has a recess (8; 8') with apertures at both ends in the longitudinal direction of the test tube (1) . 3,. The device of claim 2, c h a r a c t e r ¬ i z e d in that the mass (9) placed in the recess (8; 8') is viscous or fine granular. 4. The device of claim 2 or 3, c h a r a c ¬ t e r i z e d in that the separating body (5) has a cup-shaped recess ( 6; 6') at one of its ends which is connected to the recess by way of a passage (7) or aperture (7' ) . 5. The device of any of claims 2-4, c h a r ¬ a c t e r i z e d in that the recess (8) has a cy- lindrical shape. 6. The device of any of claims 2-4, c h a r ¬ a c t e r i z e d in that the recess (8') has a coni¬ cal shape . 7. The device of claim 2 or 3, c h a r a c - t e r i z e d in that the separating body has a sphe¬ rical primary shape.

Inventors: ERSSON NILS-OLOF, ERSSON, NILS-OLOF
Applicants: ERSSON NILS OLOF, ERSSON, NILS-OLOF
Application year: 1986
Main classification: G01N33
IPC codes: G01N33