Determining a person's blood group is important, for example in the case of blood transfusions or to test for potential Rhesus incompatibilities during pregnancy.

A common way to quickly determine a person's blood type is based on agglutination. Blood from a patient is mixed with antibodies that were pre-spotted on a specific test card called Eldon card (Figure 1). This card contains specific antibodies against antigens A (Anti-A) and B (Anti-B) as well against the Rhesus (Rh) factor antigen D (Anti-D). On every card there is a fourth area that is left empty and used as a control to make sure that the experiment kit worked correctly.

A completed blood typing test card. Three circular fields appear at the top of the card, labelled from left to right: Anti-A, Anti-B, and Anti-D. Blood clotting has occurred in the fields Anti-A and Anti-D, while no clotting occurred in the Anti-B field. Below the circles, the card is filled out with patient information such as name and date of birth, and the blood group result, which is A positive on this card.

Figure 1: Example of an Eldon Card.

If the tested blood contains the corresponding antigen to the specific antibody in the cycle, blood clots will be formed. Go to blood typing results to see all possible results of the blood typing test.