Comparison of two enzyme-linked immunosorbent assays for antigen quantitation: direct competition and antibody inhibition.

Two enzyme-linked immunosorbent assays for antigen quantitation, direct competition and antibody inhibition, were used to measure rabbit immunoglobulin G in polystyrene microtiter plates and were compared for sensitivity and reproducibility. Both procedures repetitively detected this antigen in the 1- to 100-ng/ml range. Both procedures were predictably reproducible, with direct competition procedures having steeper slopes in ranges tested. Antibody inhibition does not require conjugated antigen and can detect sample antigens if available stock antigens can be passively bound to a solid-phase polystyrene plate.