An acute hemolytic transfusion reaction caused by an anti‐P 1 that reacted at 37°C

BACKGROUND: Hemolytic transfusion reactions (HTRs) due to anti‐P 1 have rarely been reported. There is only one report (from 1945) of an acute HTR due to anti‐P 1 . CASE REPORT: A 74‐year‐old woman with anti‐P 1 was given blood that had been found to be compatible by the use of prewarmed serum and saline‐suspended red cells (RBCs) and of an antiglobulin test with anti‐IgG. The test mixtures were not centrifuged or inspected for agglutination after the 37°C incubation phase. After transfusion of 50 mL of P 1 + blood, the patient had an acute HTR (hemoglobinemia, hemoglobinuria, and increased blood pressure, temperature, and respiration). RESULTS: When studied by a reference laboratory, the anti‐P 1 was shown to be easily detectable (3+ agglutination) by a prewarming technique (saline or low‐ionic‐strength saline [LISS]), which included centrifugation at 37°C, but only weak reactions were observed when centrifugation after 37°C incubation was omitted. The indirect antiglobulin test was weakly positive (1+) with anti‐IgG, but polyspecific anti‐human globulin reacted 2+. The anti‐P 1 agglutinin was IgM, and its titer was 16 at 37°C (prewarmed) and 256 at 23°C; it caused hemolysis of RBCs at 37°C under conditions known to enhance hemolysis. An indirect monocyte monolayer assay gave results of 11.2 and 22 percent in testing of P 1 + RBCs incubated with the patient's serum alone and with patient's serum plus fresh normal serum (as a source of complement), respectively (normal ≤3%). CONCLUSION: An acute HTR was caused by a hemolytic anti‐P 1 that reacted at 37°C. This antibody was not detected by the hospital in a prewarmed crossmatch that omitted 1) the addition of LISS, 2) the reading for agglutination after the 37°C incubation, and 3) the use of antiglobulin sera containing anti‐complement.