ABO Blood Group determination for compatibility analysis in blood transfusion.

Blood banks are responsible for collecting, processing and storing blood from donors that is used for blood transfusions.

Prior to a transfusion, a compatibility test must be carried out between the blood groups of the donor and the recipient, since a transfusion between incompatible individuals will lead to agglutination of the recipient’s blood, sometimes leading to the death of the patient.

Blood groups and their importance in transfusions

The different blood groups are determined by the expression of certain antigens on the surface of erythrocytes or red blood cells (RBCs); up to date 3,000 different blood groups are known in the population.

In the context of transfusions, the antigens commonly tested for are the A antigen and the B antigen (ABO system), as well as the D antigen (Rh system).

In addition, on some occasions, in parallel to the antigen analysis, what is known as the reverse ABO test is performed, which consists of analyzing the presence or absence of antibodies against the A and B antigens in the patient’s serum. Thus, a patient whose RBCs express only A antigen could present anti-B antibodies in serum (depending on whether or not they have been previously exposed to the B antigen or another similar antigen), but in no case will they present anti-A antibodies.

The “tube test”

There are a wide variety of tests for the analysis of blood groups, one of the most common being the “tube test”, which analyzes both the expression of the A, B and D antigens by the RBCs, as well as the presence of anti-microbial antibodies. anti-A and anti-B in the serum (reverse ABO test).

Thus, the first step for carrying out the “tube test” consists of separating the RBCs from the serum, from a whole blood sample. To do this, 5 mL of whole blood is taken in a tube without anticoagulant and centrifuged at 1,500 G for 15 minutes. After centrifugation, the sample is divided into two fractions. The upper fraction, with a yellowish appearance, corresponds to the blood serum; and the lower fraction, with a reddish appearance, to the RBCs [Figure 1].

More in detail, for the analysis of the expression of antigens A, B and D, the isolated RBCs are diluted in a saline solution until obtaining a suspension with a concentration of 2-3% of RBCs. Then, a drop of this suspension (40μL) is taken and mixed with a drop of the corresponding reagent (40μL) in a microtube (0.2mL). The reagents are anti-A, anti-B and anti-D antibodies.

The tube is centrifuged at 1,000 G for 20 seconds, after which any pellet that has formed in the centrifugation is resuspended, and observed for agglutination. Finally, the agglutination results of this test are complemented with the agglutination results of the reverse ABO test, and the patient’s blood group is determined.

Centrifugation is a fundamental process in blood bank laboratories, as it allows, among other things, to easily perform compatibility analyzes in the context of blood transfusions.

To carry out all these necessary centrifugation steps, we can count on the Unicen 21, which offers multiple rotor options to work with a wide range of volumes. Its control allows customizing the way of working to integrate perfectly into laboratory processes.