Detection of red blood cell antibodies using bacterial antiglobulins: a new assay [abstract]

ABSTRACT

OBJECTIVE: To develop an agglutination technique using Staphylococcal protein A (SpA) and Steptococcalprotein G (SpG) to detect human red blood cell antibodies. METHODS: Blood samples were obtained from the National Transfusion Service of Jamaica. SpA, SpG, and anti-IgG, -C3d were commercial preparations. SpA and ApG were incubated with sensitized human red blood cells (RBC) to assess their RBC agglutinating capacity. The Ouchterlony technique was used to determine binding between the bacterial antigens and the IgG in human serum. Polyethyleneglycol (PEG) was used as an agglutination enhancer. Agglutination techniques for a large number of samples were developed, using 96 percent well polystyrene microplates and a microscope for visualizing the agglutination techniques to detect human anti-RBC IgG was compared with the traditional Coombs' test. Sensitivity and specificity were determined. RESULTS: SpA and SpG did not appear to cause agglutination of the red cells sensitized in vivo and in vitro. However, no precipitation bands were formed between human serum and the supernatant obtained after reaction of the sensitized RBC with SpA and SpG (Ouchterlony technique). These results indicated that indeed there was binding of SpA and SpG with the sensitized cells since they were not available for binding with human serum. In additon, SpA and SpG agglutinated the sensitized red blood cells in the presence of the PEG. When compared to the Coombs' test, the following results were obtained with new techniques. For the direct method, sensitivity was 93.8 percent and 95.1 percent for SpA and SpG respectively (n= 81), and specificity was 91.4 percent and 93.5 percent for SpA and SpG, respectivley (n= 93). For the indirect method, sensitivity was 96.3 percent and 97.5 percent for SPA and SpG, respectively (n= 81) and its specificity was 100 percent for both proteins (n= 85). CONCLUSION: Agglutination techniques using SpA and SpG constitute alternative and feasible tests for the detection of human red blood cell antibodies. (AU)