Blood type tests are done before a person gets a blood transfusion and to check a pregnant woman′s blood type. The following table shows the compatibility of blood types between blood donors and recipients.
Read the table as follows: A person who has A–negative blood can receive A–negative or O–negative blood. Minor antigens (other than A, B, and Rh) on the red blood cells are also checked for a match before a blood transfusion.
What affects the test?: Reasons for not able to have the test or why the results may not be helpful include: Having a recent X–ray test with contrast material, Taking methyldopa, levodopa, or some antibiotics, such as cephalexin. These medicines may cause a false Rh–positive result, Having a blood transfusion in the 3 months before the blood type test, Having cancer or leukemia, Having a bone marrow transplant.