Comparison of enzyme-linked immunosorbent assay and radioimmunoassay for determination of anti-pneumococcal polysaccharide antibodies.

Antibodies against pneumococcal capsular polysaccharide types 1, 3, 6A, 7F, 8 and 9N were determined before and 4 weeks after pneumococcal vaccination by both enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay (RIA) in 49 children, 42 of whom had been splenectomized. Using linear regression analysis a significant correlation between total antibody concentrations determined by ELISA and RIA was found for all 6 antigens (p less than 0.001 for each). The degree of correlation varied between types, antibodies against type 3 showing the best concordance, those against type 6A the poorest. In 84% of the samples assayed both the RIA and the ELISA determined antibody concentrations were either above (55%) or below (29%) the hypothetical protective antibody concentration.