Naturally Occurring Anti-D in a Male Blood Donor, Unresolved Mystery

In accordance with numerous national and international criteria, screening donated blood for abnormal antibodies against red cell antigens is crucial for patient safety. Antibodies can be formed by three mechanisms: by immune responses, naturally occurring, or passively acquired. In accordance with departmental policy, ICT was performed on a 30-yearold male blood donor's sample in addition to ABO Rh grouping. He tested A Rh Dnegative and had a positive ICT (+ 2). Anti-D was identified by using the antibody screening and identification panel. Retesting revealed similar results, so we called the donor. We were unable to find a source for the Rh isoimmunization during the course of his history. On further work-up, we found that antibodies reacted only in the antiglobulin phase with no reaction in the saline phase, suggesting an IgG type of antibody. Also, the anti-D titers (IgG) of the donor were up to 1:32. All potential sources of Rh isoimmunization have been ruled out for a male donor. Therefore, we assume that this donor has naturally occurring anti-D, perhaps created by certain environmental factors, bacteria, or components of the COVID vaccine that have cross-reactivity with the D antigen. This instance emphasizes how crucial the ICT test on the donor blood is. In our case, all potential causes of alloimmunization were ruled out, leaving only exposure to antigens with antigenic similarity to D antigens as a viable explanation.