Blood Group: MNS

Common: 45% Caucasians, 69% Blacks are at risk for developing anti-S.

Causes HDN: Yes
Critical Titer: 1:16
Anti-S is more common than anti-s, but both can cause severe HDN [1]. Anti-S is capable of causing rapid red blood cell destruction [5].

Anti-S can be naturally occurring [2]. Because anti-S is naturally occurring, the father needs to be tested for the S antigen. It is possible that both parents could be negative for S, in which case, the anti-S would be naturally occurring and would not harm the baby because the baby would be negative for S like both parents. 

Anti-S that is not naturally occurring, but that occurs because of blood mixing, can be fatal [3]. In 1952 there were two examples of anti-S causing HDN, one of which was fatal [3]. Despite the potential to be very severe, anti-S is not always fatal. An infant with anti-S experienced a hematocrit drop and rise in bilirubin but required no treatment [4].


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