Undetectable IgG4 in immunoprecipitation: association with repeated infections in children?

A total of 210 patients with repeated infections were screened for IgG4 deficiency. In 30 patients (14%) IgG4 was undetectable by radial immunodiffusion (less than 30 mg/l). Of these patients 17 (57%) were less than 2 years of age. Concomitant IgA deficiency (IgA less than 0.05 g/l) was demonstrated in 11 cases (37%). IgG2 serum levels below the normal range were found in 26 children. IgG4 could be demonstrated at a concentration of 0.5-29 mg/l in all 30 patients using a more sensitive enzyme-linked immunosorbent assay technique. Although a highly selected group of patients was investigated, the percentage of individuals without detectable IgG4 by immunodiffusion was in the same range as reported in the literature for healthy control persons. It is thus concluded that IgG4 serum reference levels have to be defined using more sensitive methods and that the observed severe infections are more likely to be connected with low serum IgG2 and/or IgA levels than undetectable IgG4 as measured by immunodiffusion.