[Level of total serum IgG4 using ELISA].

We report on an indirect competitive immunoenzymatic assay (ELISA) for the determination of serum total IgG4 levels. This procedure allows accurate and sensitive measurements. Normal values vary according to age and sex, with mean normal levels of 22.3 +/- 14.6 mg/dl in adults. Serum IgG4 levels observed in atopic subjects are not significantly different from those in age and sex matched normal subjects. However, IgG4 levels are significantly increased in hay fever and honey bee sensitization. Measurement of serum total IgG4 levels clearly needs to be combined with the evaluation of specific anti-allergen antibodies of this subclass in investigations of the possible reaginic or blocking activity of IgG4 antibodies.