Harvard Men's Health Watch

On call: Blood type and your health

Q. At my last office exam, I asked my doctor if he could tell me my blood type. I was surprised it was never checked as part of my routine lab tests. Isn't my blood type important for the doctor to know?

A. I am not surprised that your doctor did not check your blood type as part of routine testing. Blood type does not influence doctors' decisions about your preventive health or how to treat common chronic health conditions. Blood type is important to know in only two situations: blood transfusions and tissue or organ donations.

Blood type varies according to the different kinds of sugar molecules and proteins on the surface of red blood cells. These inherited differences combine to form eight distinctive blood types, from O positive (the most common one in the United States) to AB negative (the least common).

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