Abstract: Objective： To investigate serum IgG4 levels in different diseases and the changes of serum IgG4 levels in post  treatment of IgG4 related disease. Methods: Clinical data of 620 patients who received investigation of serum IgG4 in Peking University People’s Hospital from January 1, 2015 to March 31, 2016 were collected retrospectively. According to the difference of the diseases ,they were divided into common group of diseases, autoimmune diseases and IgG4 related diseases; pancreatic disease patients were divided into autoimmune pancreatitis and pancreatic cancer group; According to different treatment stages of the disease, the patients with IgG4 related diseases were divided into pretreatment group and post treatment  group. And  the expressions of the patients’ serum IgG4 levels in different groups were analyzed. Results: The median serum IgG4 level in the group of the patients with common diseases was 0.480（0.005， 50.400） g/L, in the group of autoimmune disease was 0.406 （0.003， 18.700） g/L , in the group of IgG4 related diseases was 5.200（0.046， 46.000）g/L, which was significantly higher in the group of IgG4 related diseases than the other two groups, and there was obvious statistical significance in serum IgG4 levels between the group of IgG4 related diseases and  the other two groups (P<0.01); There was no obvious difference in serum IgG4 levels between the common disease group and the autoimmune disease group, and there was no obvious statistical difference in serum IgG4 levels between the two groups (P>0.05)．In the patients with IgG4 related diseases, the median serum IgG4 level in the group of pretreatment  patients was 6.540 （1.330， 34.100） g/L , and 3.735 （0.063， 46.000） g/L in the post treatment patients.   Serum IgG4 levels decreased in post treatment group, significantly lower than in pretreatment, there was obvious statistical difference in serum IgG4 levels between the two groups (P<0.01)．The median serum IgG4 level in the group of patients with autoimmune pancreatitis was 3.735 （0.063， 46.000） g/L ,and 0.438 （0.056， 1.130） g/L in the group of patients with pancreatic cancer，which was significantly higher in the group of patients with autoimmune pancreatitis than the others, and there was obvious statistical difference in serum IgG4 levels between the two groups (P<0.01). Conclusion: Serum IgG4 levels in patients with different diseases were different, and were significantly higher in patients with autoimmune pancreatitis and IgG4 related diseases, so serum IgG4 levels can provide the basis for the differential diagnosis of different diseases; Serum IgG4 levels in patients with IgG4 related diseases decrease significantly after treatment, so it can be used as an important index to evaluate the curative effect of IgG4 related diseases.

Key words: IgG4, IgG4 related disease, Autoimmune diseases, Serum