Ickle Dorritt: In the states that require pre-marriage blood tests (I'm not sure that all of them do) they are testing for diseases or traits that would affect potential offspring of the couple (sickle cell trait in either, or negative blood type, syphilis, or rubella in the mother). In some states, such as Indiana, the premarital blood test is only required of women who are of childbearing age. I guess it's done on the principle that many people will wait until marriage to start a family, and that if there is a reason why you and your future spouse should be cautious about having children, it's best to know that beforehand so that it can be treated or special precautions can be taken. What's actually tested for varies from state to state. The only thing that Indiana tests for is Rubella.