Abstract
The indirect antiglobulin test (IAT) often registers as a false positive with enhancing reagents in screening test for irregular antibodies and cross-match test in response to the presence of cold antibodies. Since cold antibodies do not cause a transfusion reaction, IAT without enhancing reagents, 60-min IAT is useful in distinguishing clinically significant antibodies. We recently experienced a rare case in which 1×and 2×-diluted samples showed negative results, while 4×-diluted samples showed positive results on 60-min IAT. IgM type anti-M was produced at a patient's first pregnancy, and IgM+IgG type anti-M was produced after the first child delivery. At the third pregnancy, anti-M titer was monitored every two weeks until the day before delivery. Titer of anti-M increased to 1: 64, but findings for 1: 1-2 dilution serum of the patient were negative on 60-min IAT at 37 weeks into the pregnancy. Flow cytometry analysis revealed that IgM type anti-M reacted more strongly at 37°Cthan at lower temperatures. These findings suggested that anti-IgG globulin serum was unable to be used to build bridges, resulting in the negative results on IAT because IgM type anti-M, which reacted at 37°C, inhibited the binding of IgG type anti-M. The present case has shown the importance of using dithiothreitol or 2-mercaptoethanol, which destroys IgM type antibody, for the detection of clinically significant antibodies.
