What is the D antigen (Rh factor) in the blood?

D antigen is a protein with many parts, found on the surface of red blood cells. The D antigen is also known as the "Rh factor," and it tells your blood type. People are either D (Rh) negative or D (Rh) positive. If your blood type is D negative, your red blood cells do not have the D antigen.

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