[Divergence between measured values of total IgG and subclass IgGs (sum of IgG1-IgG4) in IgG4-related disease]

In systemic IgG4-related disease, an elevation of the serum IgG4 level(IgG4: 135 mg/dl or higher) and IgG4-positive plasma cell infiltration occurs. Since the total IgG and sum of subclasses, IgG1 through IgG4, were markedly different in a patient suspected of having Mikuliez's disease, we investigated the relationship between total IgG and sum of IgG subclasses. The subjects were healthy individuals, and low IgG4, high IgG4, hyper-gamma globulinemia and hypo-y globulinemia groups. Total IgG was measured using 'N-assay TIA IgG-SH' (Nittobo) and Hitachi 7700, and IgG subclasses were measured using BS-NIA reagent (Binding Site) and BN II (Siemens). Designation of total IgG and the sum of IgG subclasses was established in the healthy control subjects. However the total IgG level and sum of IgG1-4 levels were different when the balance among the IgG subclasses was lost. In case such as :1) the IgG4 level was high and 2) IgG1-type M protein was present. These results indicate that the reevaluation of measured data is necessary when the IgG4 concentration is high and the difference between total IgG concentration and the sum of IgG subclasses is large.