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Blood Typing

Determination of Human ABO Blood Type Via Antigens Present in Saliva



Red blood cells (RBC) can be grouped into A, B, O, and AB blood types. The designations of A, B, AB, and O describe the presence or absence of two antigens on the surface of the cell. Blood typing uses antibody serum which will bind to the antigens making the RBCs clump together. The test is normally done with a small sample of blood from the subject which is then mixed with A antibodies and B antibodies. The blood type is then derived from the clumping of the two mixtures.

Our investigation uses a more complicated scheme which depends on antigen excretion in saliva. By combining these free antigens with antibodies then appropriate RBCs, we can also determine the blood type. The method does not work with all individuals.

The motivation behind blood typing is to avoid immune response during transfusion. Normally, the A type RBCs float in blood plasma where B type antibodies are present. If B type RBCs are added, the B type antibodies attach to the new RBCs and begin to clump. Conversely, if B type RBCs float in blood plasma, with naturally occuring A type antibodies, and A type RBCs are added, then the new RBCs clump. The other blood types AB and O designate combinations of the A and B type RBCs. The AB type RBC has both A and B antigens thus obviating the presence of any antibodies. The O type RBC has neither A nor B antigens thus the plasma has both A and B antibodies. By avoiding the clumping of RBCs, doctors can transfuse blood without causing a horrible immune response and blockage of capillaries and arteries.


The saliva is processed extensively in order to preserve and extract the antigens, if present. The saliva is first placed in a boiling bath which will denature the enzymatic proteins which could break down the antigens. Then the salive was centrifuged to separate the cells and the debris. The supernantant was the used and serially dilluted with saline solution. Each sample consisted of 100 L of saline solution and 100 L of the previously diluted solution. Each solution was mixed by the micropipet. The samples were then frozen to prevent further decay of the antigens.

On the second lab day, the tubes were thawed and 100 L of the respective antiserum were added. The tube was mixed and allowed to stand. Then, RBCs which would react with the antiserum were added. After shaking, the tubes were allowed to stand. We observed for clumping in the tube.


    Control  2    4   8    16   32   




Results and Analysis