The measurement of platelet-associated IgG by a microplate quantitative antiglobulin consumption assay using automated through-the-well spectrophotometry.

A microplate modification of the quantitative antiglobulin consumption assay (QACA) has been developed for the measurement of platelet-associated IgG (PAIgG). This method employs an automated through-the-well absorbance spectrophotometer (microplate reader) to directly measure the hemolysis of target indicator cells (IgG-coated sheep erythrocytes) in an assay performed entirely in a 96-well microtiter plate. PAIgG measured by this method in 54 thrombocytopenic patients and 17 controls correlated highly (r = 0.94) with results obtained by the standard tube assay procedure. By substantially simplifying the performance of the QACA and increasing its sensitivity by nearly 1 order of magnitude, this method permits the rapid quantitative determination of PAIgG on platelets obtained from as little as 1 to 4 ml of whole blood.