AN EDTA-ASSOCIATED ANTI-B AGGLUTININ - THE ROLE OF IONIZED CALCIUM

BACKGROUND: It is believed that EDTA-dependent panagglutination is ass ociated with free carboxylic acids that support reactions of rare auto agglutinins. CASE REPORT: An ABO typing discrepancy occurred in an 88- year-old patient. The specificity of his autoagglutinin was demonstrat ed by panel cell study and absorption tests using normal donors' red c ells or immunoadsorbents coated with A, B, or O substances. Inhibition assays were performed to determine whether the autoagglutinin was inh ibited by ionized calcium Or carboxylic acids. The autoagglutinin had anti-B specificity when tested in the presence of EDTA. It was neutral ized by group B secretor saliva and adsorbed by crystalline silica coa ted with simple B substances with or without EDTA, although it was abs orbed by group B red cells only in the presence of EDTA. The agglutina ting activity was stronger at 25 degrees C (titer 64) than at 37 degre es C (titer 16) and was destroyed by treatment of the serum with dithi othreitol, which suggests that the autoagglutinin is IgM. This activit y also appeared in the patient's serum after dialysis and in an eluate obtained after adsorption with simple B substances, and it was inhibi ted by the addition of CaCl2 at 0.5 mM or higher concentrations. This suggests that the agglutination is not dependent on EDTA but, rather, on the concentration of ionized calcium. The autoagglutinin failed to react with group B red cells treated with glutaraldehyde for 10 minute s. CONCLUSION: An anti-B autoagglutinin was shown to have caused an AB O typing discrepancy in the presence of EDTA. These results suggest th at autoagglutination requires an environment with low levels of ionize d calcium, but not the presence of carboxyl groups.