Auto-anti-M antibodies are not commonly documented serologically. A review of the literature reveals only ten cases with no consistent clinical or laboratory findings. In their institution, over a 12-year period, the authors have identified this autoantibody in seven patients, suggesting that it may not be such a rare entity but rather may be underdiagnosed. In this article the authors describe the pertinent clinical and serologic findings in their seven patients, as well as review the salient features of the previously reported cases.

We present the differential diagnosis for a Coombs-positive immune hemolysis having onset during hospitalization and, in particular, during the postoperative period. The stimulus for this article was a delayed hemolytic transfusion reaction (DHTR) due to anti-U following open-heart surgery. The initial clinical and serologic findings led us to consider other causes of immune hemolysis which are reviewed in this article. To our knowledge, this is the fourth case of a DHTR due to anti-U to be reported in the medical literature. ImmunohematoIogv 1993;9:41-46.