Clinical Significance of Serum IgG4 in the Diagnosis and Treatment Response of IgG4-Related Disease in Adults of Southwest China: A Retrospective Study.

Background: There is no standard cut-off value of serum IgG4 concentration and serum IgG4/total IgG ratio for the diagnosis of IgG4-related disease (IgG4-RD) or as a marker of treatment responses. We aimed to explore this issue through a retrospective cohort analysis of adults in southwest China.

Methods: The diagnostic performance of serum IgG4 concentration and IgG4/IgG ratio for IgG4-RD was evaluated in a retrospective analysis of 177 adults newly diagnosed as having IgG4-RD and 877 adults without IgG4-RD. Dynamic analysis was performed to evaluate the significance of serum IgG4 concentration on IgG4-RD treatment responses.

Results: The serum IgG4 concentration differed according to sex. The optimal cut-off values of serum IgG4 concentration and IgG4/IgG ratio for IgG4-RD diagnosis were 1.92 g/L and 0.12 in males and 1.83 g/L and 0.11 in females, respectively. For patients with serum IgG4 concentration >2.01 g/L, the cut-off values in the total population were >3.00 g/L and 0.19, respectively. The median serum IgG4 concentration decreased over time, and the decrease rate increased over time. The serum IgG4 concentration significantly decreased at >1 week post-treatment (P=0.004), and the median decrease rate was close to 50% at >4 weeks post-treatment.

Conclusions: Serum IgG4 can be a good indicator for IgG4-RD diagnosis; however, different diagnostic cut-off values should be determined according to sex. The decreasing rate is more conducive than the serum IgG4 concentration to monitor treatment efficacy. The IgG4/IgG ratio did not improve the diagnostic efficacy for IgG4-RD.