Apparent change of Rhesus blood group typing in a case of ulcerative colitis

An interesting case of ulcerative colitis with an apparent change of Rhesus blood group typing is described. To our knowledge, this has not been reported before. We postulate that during the initial active phase of ulcerative colitis, an unknown D-like antigen, possibly bacterial in origin, could temporarily give rise to a Rhesus D-positive blood group typing in a patient with Rhesus D-negative blood type. Interestingly, with continuous immunosuppressive therapy for ulcerative colitis, the patient did not develop anti-D antibodies despite multiple transfusions with D-positive blood.