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Human blood is typed according to whether certain markers, called antigens, are present on the surface of red blood cells. The ABO system classifies blood as type A, B, AB, or O based on the presence or absence of the A and B antigens; the Rh system classifies blood as negative or positive based on the presence or absence of the Rh antigen (Rh factor).
If red blood cells have:
Rh blood typing determines the presence (+) or absence (–) of the Rh factor. If red blood cells:
Last Revised: October 27, 2011
Author: Healthwise Staff
Medical Review: E. Gregory Thompson, MD - Internal Medicine & Brian Leber, MDCM, FRCPC - Hematology
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