Effect of delayed centrifugation or reading on the detection of ABO incompatibility by the immediate-spin crossmatch.

The immediate-spin (IS) crossmatch is a method that detects ABO incompatibility. However, under certain circumstances, this test may show unwanted negative or weak results, even though the red cells (RBCs) and serum being tested are ABO incompatible with each other. The present study investigated the potential effect of delayed centrifugation or reading on the IS crossmatch test performance. When the centrifugation step of the IS crossmatch between group O sera and group A1 RBCs was delayed for 2 minutes, 5 of 200 crossmatches showed no agglutination with only trace (n = 2) or moderate (n = 3) hemolysis, and one crossmatch showed only weak, macroscopic agglutination, but moderate hemolysis. All six sera contained A antibodies that were lytic in vitro and, therefore, probably were capable of causing in vivo hemolysis of transfused A1 RBCs. Delaying the reading of the IS crossmatch test for 2 minutes had no apparent effect on test performance. These data demonstrate the importance of technologists' recognition of hemolysis as a positive result on IS crossmatches, especially if the performance of the centrifugation step of the test is delayed. Furthermore, the unwanted negative agglutination results were abolished by suspending the group A1 RBCs in saline containing EDTA. The authors' laboratory has modified its IS crossmatch procedure so that donor RBCs are routinely suspended in saline containing EDTA before testing. This procedural change should increase the safety of the IS crossmatch.