Anti-D (-RH1) of the Rh blood group system is clinically important as it causes haemolytic transfusion reactions and haemolytic disease of the fetus and newborn. Although most people are either D+ or D-, there is a plethora of D variants, often categorized as either weak D or partial D. These two types are inadequately defined and the dichotomy is potentially misleading. DVI is the D variant most commonly associated with anti-D production and UK guidelines recommend that patients are tested with anti-D reagents that do not react with DVI. Weak D types 1, 2, and 3 are seldom, if ever, associated with alloanti-D production, so a policy recommendation would be to treat patients with those D variants as D+, to preserve D- stocks, whereas patients with all other D variants would be treated as D-. All donors with D variant red cells, including DVI, should be treated as D+.
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