Clinically significant naturally occurring anti-N and anti-S in a blood donor: a rare finding.

To the Editors: Alloimmunization is triggered when an individual whose red blood cells (RBCs) are lacking particular antigens is exposed to these antigens through transfusion or pregnancy, causing the formation of immune antibodies. In addition to these exogenous exposures, underlying inflammatory or autoimmune conditions may lead to formation of unexpected antibodies. Individual factors also play a role, since some people are responders and others are non-responders. We report a case of naturally occurring alloanti-N and alloanti-S in a healthy D+ blood donor. Both antibodies were reactive over a wide thermal amplitude and hence were potentially clinically significant. This case highlights the importance of incorporating the indirect antiglobulin test (IAT) to test for unexpected RBC antibodies for all blood units as a routine protocol.