Distribution characteristics of elevated serum immunoglobulin G4 (IgG4) and its relationship with IgG4-related disease

Abstract

Objective: To elucidate the distribution characteristics of elevated serum immunoglobulin G4 (IgG4) and its relationship with immunoglobulin G4-related disease (IgG4-RD).Methods: In total, 14 522 unique patients who were tested for serum IgG4 over a 4.5 year period were enrolled. Demographic and serological characteristics of all patients, and the range of diseases and serological characteristics of patients with elevated serum IgG4, were retrospectively analysed. Organ involvement in IgG4-RD patients and the utility of serum immunoglobulin for distinguishing IgG4-RD from non-IgG4-RD were also investigated.Results: Elevated serum IgG4 (> 1.4 g/L) was observed in 1793/14 522 patients (12.3%) and primarily appeared in middle-aged and elderly men. Only 7.3% of patients with elevated serum IgG4 met the diagnostic criteria for IgG4-RD. Elevated serum IgG4 was also found in over 30 types of non-IgG4-RD. Serum IgG4 levels were higher in IgG4-RD patients with multiple-organ involvement and were positively correlated with the number of affected organs. The diagnostic utility of serum IgG4 for IgG4-RD was higher than that of the IgG4/IgG ratio and serum IgG. The optimal serum IgG4 cut-off value for diagnosing IgG4-RD was 2.06 g/L, with a sensitivity of 95.6% and specificity of 94.7%.Conclusions: Elevated serum IgG4 may be present in multiple non-IgG4-RD conditions. However, a high serum IgG4 concentration is of great value for IgG4-RD diagnosis, and there appears to be a positive relationship between serum IgG4 levels and organ involvement in patients with IgG4-RD. Examining the IgG4/IgG ratio and serum IgG does not improve the ability of IgG4-RD diagnosis.