Micro-enzyme-linked immunoassay for the quantitation of platelet-associated IgG (PAIgG).

An enzyme linked immunoassay was developed using the microtiter system to measure platelet-associated IgG (PAIgG). One single determination needs 2 x 10(6) platelets usually obtained from 3 ml blood anticoagulated with EDTA. Platelets are incubated with peroxidase-conjugated anti-human IgG. Its unbound fraction is adsorbed to an IgG coated microtiter plate, quantitated by a colour reaction and found to be inversely related to the amount of PAIgG. Healthy donors (n = 40, aged 1 day to 35 years) possessed 3.6 +/- 2.0 (mean +/- S.D.) fg IgG/platelet. Increased levels of PAIgG were found in patients with acute (n = 16) and chronic (n = 5) idiopathic thrombocytopenic purpura. Postrecovery platelets had normal values of PAIgG. Widely varying levels of PAIgG were found in patients with freshly diagnosed acute lymphocytic leukemia.