Blood groups are of great clinical importance in blood transfusion and transplantations. The discovery of ABO blood grouping by Landsteiner is one of the most important factors in making blood transfusion practices possible.
Routine blood grouping still relies primarily on hemagglutination reactions between antigen and antibodies that are read and interpreted either manually or by automated means. The principles behind hemagglutination reactions, biochemistry of blood group antigens, and increasing knowledge of the properties of immunoglobulin associated with blood group antibodies led to the development of laboratory tests other than direct agglutination.
The quality of blood grouping reagents is clearly an important factor for safe blood transfusion, yet there is currently no appropriate international standardization of monoclonal anti-A or anti-B blood grouping reagents. Although WHO has international standards for anti-A and anti-B, they were prepared many years ago and represent grouping reagents available at that time, whereas current anti-A or anti-B grouping reagents consist of monoclonal antibody preparations.
Enough examples of monoclonal ABO antibodies have been produced, predominantly in hybridomas of murine myeloma cells and lymphocytes of mice immunized with ABO substances or with red cells. Monoclonal anti-A and anti-B have proved to be very satisfactory reagents and are generally the reagents of choice, both for manual and automated techniques.
Avidity can be considered as the speed with which the reagent will show agglutination when tested by slide technique against appropriate RES cell antigen. The accepted avidity time for an ideal anti-A reagent to show visible agglutination with 10 percent suspension of A1 cells is 10 sec, A2 cells 20 sec, and A2B cells 30 sec. The avidity time against A2B cells is important as any anti-A reagent failing to react with A2, when coupled with B could result in a misgrouping of this blood, thereby concluding it as group B instead of AB. However, the avidity time for anti-B should not be more than 10 sec when tested against group B cells.
The degree of completeness of agglutination is important when selecting suitable anti-sera. Usually, a serum of high titer activity and good avidity against A1 and B cells will show clear and visible agglutination up to a dilution 1:4; if this is not the case, the reagent should not be used for determination of blood group.
Along with avidity, specificity is also equally important while manufacturing blood grouping sera. It needs to be ensured that anti-A reagent reacts only with cells possessing anti-A and should not contain any contaminating antibodies which are capable of reacting with non-A cells. To confirm the specificity, anti-A is tested against a number of group B and O cells, whereas anti-B is tested against a number of group A1 and O cells.
The high-titer-specific anti-sera A and B may cause hemolysis of the red cells as opposed to agglutination due to presence of alpha-beta hemolysins. Hence the anti-sera are heated at 56°C for 30 min to destroy the activity of complements on which the hemolysins are dependent.
The test may appear negative as opposed to a strong positive reaction due to very high titer demonstrating the Prozone phenomenon. In these cases, there are hardly any options left other than performing the test after suitable dilution.
The potency of the blood grouping sera is affected up to a great extent, if stored at room temperature for a long time. Hence it is always advised to store it at 4°C during working days; however, it should be stored at –20°C for more prolonged periods of time, unless instructed otherwise. Some antisera are preserved using antibacterial chemicals like sodium azide used in the strength 1/10000, which increases the shelf life of the reagent.
Following the prime minister’s initiative of Make in India, Meril endeavors to manufacture and introduce anti-sera reagents for ABO blood grouping. Meril is also proud to announce the launch of reagents for anti-A1 lectin and anti-AH lectin. These reagents are being manufactured at its state-of-the-art 300,000 square feet R&D and manufacturing facility at Vapi.