The McGill Physiology Virtual Lab

Blood Laboratory

Blood typing
  The blood groups refer to the presence on human red blood cells of certain antigens, the blood group factors. One very important group of factors present on the red blood cells is the ABO system. The ABO group of a person depends on whether his/her red blood cells contain one, both, or neither of the 2 blood group antigens A and B. There are, therefore, 4 main ABO groups: A, B, AB and O.
Antibodies (agglutinins) for the antigens A and B exist in the plasma and these are termed anti-A and anti-B. The corresponding antigen and antibody are never found in the same individual since, when mixed, they form antigen-antibody complexes, effectively agglutinating the blood.

Testing for ABO Group - Procedure

One end of a slide is labelled Anti-A, and the other Anti-B. A drop of Anti-A test serum is added to the end marked Anti-A, and a drop of Anti-B serum is added to the end marked Anti-B.
One drop of blood is added to each end of the slide, and mixed well, using separate wooden sticks.
The results are read directly from the slide. The subject is blood group A if agglutination occurred with the Anti-A test serum; group B if agglutination occurred with the Anti-B test serum; group AB if agglutination occurred with both test serums, and O if there was no agglutination in either case. In the sample to the right, we conclude the subject has type A blood.

Examine the slides below and determine the blood type of the subject in each case. Click below to check your answer.





What is the answer?

When transfusing blood, it is important to remember that the donor's blood must not contain red blood cells that the recipient's antibodies can agglutinate. Theoretically, then, individuals belonging to blood group O are universal donors, while those of blood group AB are universal recipients.

The Rh System
Rh antigens, named for the rhesus monkey in which they were first discovered, are also surface antigens expressed on red blood cells. There are a few Rh antigens (common one is called D). Red cells expressing the Rh antigens are called Rh positive. Red cells which do not express this surface antigen are Rh negative (about 15% of the human population is Rh negative).

Rh system becomes important when one considers the eventuality of Rh incompatibility between mother and fetus; in such a case, the antibody-mediated cytotoxicity mechanism involved threatens the well-being of the fetus.
During birth, a leakage of the baby's red blood cells often occurs into the mother's circulation. If the baby is Rh positive (inheriting the trait from its father) and the mother is Rh negative, these red cells will cause the mother to manufacture antibodies against the Rh antigen. The antibodies (IgG class) do not cause problems for that first born, but can cross the placenta and attack the red cells of a subsequent Rh+ fetus. The red cells are destroyed, leading to anemia and jaundice. The disease - erythroblastosis fetalis or hemolytic disease of the newborn- may result in fetal death.

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