1. Field of the Invention
The continued dependence upon whole blood obtained from individuals for replenishing blood in another person requires the monitoring of large numbers of blood samples for their blood group type. In determining the blood group, one is interested in a number of factors: The particular ABO group; the presence of antibodies to the antigens of the ABO group; and the Rh type. Where each of these factors must be determined independently, a large number of tests are involved. For the most part, hemagglutination tests have been involved in measuring the various factors, which are subjective labor intensive and cumbersome. Furthermore, instruments for automated testing are available but these instruments are expensive and designed for large numbers of tests. It is therefore desirable to find techniques which allow for minimal numbers of determination and automation of the method of determination, while accurately reporting the information necessary for blood typing.
Specific antibodies to cell surface antigens other than the A and B blood group antigens are commonly found in 1-2% of human blood samples. The presence of these antibodies in a blood transfusion recipient may cause an adverse reaction if the blood that is transfused contains cellular antigens complementary to the recipient's antibodies. It is, therefore, necessary to test recipient blood for such antibodies. Normally, this is done by combining the serum or plasma of the recipient with "test cells" that are known to carry the relevant antigens on their surface. After incubation of this mixture, the cells are separated, washed free of the serum or plasma, and incubated with anti-immunoglobulin. This reagent, often called Coombs' reagent, binds to any recipient antibodies that are bound to the cells and causes the cells to agglutinate. Agglutination therefore indicates that the antibody screen is positive. Since the ability of the Coomb's reagent to cause agglutination can be blocked by patient immunoglobulin that is present if washing is incomplete, it is necessary to carry out a positive control when no agglutination of the test cells occurs. This may be done by separating the test cells from the solution containing the anti-immunoglobulin by centrifuging such solution and then adding to the solution "control cells" that are presensitized, that is, they have human antibodies bound to them. Usually, the control cells are prepared by incubating Rh positive cells with anti-Rh antibodies. If patient immunoglobulin has been removed and anti-immune globulin is present, the control cells will agglutinate and the test will be deemed valid. If they do not agglutinate, a negative antibody screen result indicated by the absence of agglutination the test cells is considered invalid.
The above described positive control for antibody screen requires that a solution containing the test cells be centrifuged or that the test cells be otherwise separated from the anti-immunoglobulin solution prior to addition of the control cells. This is considered necessary because of difficulty in observing test cell agglutination in the presence of control cells.