Weak D Phenotype
Those with weak D were traditionally thought to have completely normal but significantly decreased amounts of D antigen on their RBCs (note that this is in contrast to classic partial D, in which the person is assumed to have abnormal D antigen in normal amounts on their RBCs). Weak D and partial D are in fact not as separate as we would like to think from the above “classic” definitions. There are overlap categories with decreased quantities of D having qualitative abnormalities (which some call “weak partial D” or “partial weak D”). As a result, the AABB recently recommended that blood recipients and pregnant females with weak D be tested with Rh genotyping to define their D variant in a more precise manner (potentially conserving the Rh negative blood supply and reducing the number of unnecessary RhIg injections).
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