The diagnostic significance of serum IgG4 levels in patients with autoimmune pancreatitis: a UK study.

Background: Autoimmune pancreatitis (AIP) is recognised as an end organ manifestation of the systemic condition known as IgG4-sclerosing disease. One major characteristic of this disease, regardless of its location in the body, is the presence of high levels of circulating serum IgG, in particular IgG4 antibody. In the case of AIP, differential diagnosis from other conditions of the pancreas and biliary system, particularly cancers, can be difficult, but could result in avoiding invasive procedures and surgery. Earlier studies have evaluated the use of checking IgG4 levels in AIP diagnosis; these have produced variable results.

Objective: To further assess the diagnostic significance of serum IgG4 levels in AIP and investigate its value in differentiating from cancer of the gastroenterological system.

Methods: A retrospective study of 196 IgG4-requested samples from a 24-month period was examined. Samples were sorted into confirmed AIP, cancer or other pancreatic conditions including primary sclerosing cholangitis.

Results: Patients with AIP possessed a mean serum IgG level that was significantly higher compared with all other groups (mean serum IgG level=19.0 g/l+/-2.5, P<0.001). The mean serum IgG4 level of AIP patients was also significantly higher compared with all other conditions including cancer patients (mean IgG4 level=3.7 g/l+/-0.5, P<0.001).

Conclusion: This data lends support to circulating IgG4 levels only being used as an accompanying diagnostic marker to imaging, histology and clinical presentation. In particular, this may help in differentiating between AIP and pancreatic carcinoma.