Measurement of serum IgG4 levels by a competitive immunoenzymatic assay with monoclonal antibodies.

A competitive indirect ELISA is described for the measurement of IgG4 levels. It uses a monoclonal anti-subclass and antibody and purified monoclonal IgG4 as standards. This method is sensitive and reproducible and more accurate than hemagglutination inhibition and radial immunodiffusion. Serum IgG4 levels in 173 normal adults were less than 0.01-2.1 mg/ml (mean 0.30 mg/ml) in women and less than 0.01-1.87 mg/ml (mean 0.465 mg/ml) in men.