Abstract:

Objective To investigate the diagnostic efficacy of different serum IgG4 thresholds for IgG4-related diseases（IgG4-RD）. Methods From January 2013 to July 2021，5 059 patients who received serum IgG4 determination for the first time in the Affiliated Huaian No.1 People's Hospital of Nanjing Medical University，Northern Jiangsu People's Hospital and Xuzhou First People's Hospital were enrolled. There were 38 patients with IgG4-RD（IgG4-RD group） and 5 021 patients without IgG4-RD（non-IgG4-RD group）. Totally，131 healthy subjects from the First Affiliated Hospital of Huaian，Nanjing Medical University were enrolled as healthy control group. Serum IgG4 levels were determined by immunoscattering turbidimetry. Receiver operating characteristic（ROC） curve was used to evaluate the differential diagnosis of IgG4-RD by IgG4. The differential diagnosis of IgG4-RD with different IgG4 thresholds was analyzed. Results Among 38 patients with IgG4-RD，35（92.1%） cases had IgG4>1.35 g·L^-1，and 34（89.5%）cases had IgG4>2.01 g·L^-1. Multiple organs were involved in 23（60.5%） cases. Of the 5 021 non-IgG4-RD patients，430（8.6%） cases had serum IgG4>1.35 g·L^-1，and 203（4.0%） cases had serum IgG4>2.01 g·L^-1. Serum IgG4 levels were increased successively among healthy control group，non-IgG4-RD group and IgG4-RD group（P<0.001）. The area under curve（AUC） for the differential diagnosis of IgG4-RD was 0.971，the optimal threshold was 1.59 g·L^-1，the sensitivity was 92%，and the specificity was 94%. In the differential diagnosis of IgG4-RD，the sensitivity and specificity were 92% and 91% when the threshold of IgG4 was 1.35 g·L^-1，and they were 92% and 92% when the threshold was 1.40 g·L^-1，respectively. When the threshold was 2.01 g·L^-1，the sensitivity and specificity were 89% and 96%，and when the threshold was 2.80 g·L^-1，the sensitivity and specificity were 79% and 97%，respectively. Conclusions Increased levels of IgG4 are seen not only in IgG4-RD patients，but also in non-IgG4-RD patients. Appropriate IgG4 thresholds should be established to assist clinical diagnosis of IgG4-RD.

Key words: IgG4, Threshold, IgG4-related disease, Autoimmune disease