Serum Level of Ca 19-9 Increases Ability of IgG4 Test to Distinguish Patients with Autoimmune Pancreatitis from Those with Pancreatic Carcinoma

Autoimmune pancreatitis (AIP) is often difficult to distinguish from pancreatic carcinoma or other pancreatobiliary diseases. High serum levels of carbohydrate antigen 19-9 (Ca 19-9) are indicative of malignancies, whereas high levels of immunoglobulin (Ig)G4 (> 1.4 g/l) are characteristic of AIP. We investigated whether serum levels of these proteins can differentiate between these diseases. We measured levels of Ca 19-9 and IgG4 in serum samples from 33 patients with AIP, 53 with pancreatic carcinoma, and 145 with other pancreatobiliary disorders. We determined cut-off levels for each assay. Logistic regression analysis was used to evaluate combined data on Ca 19-9, IgG4, and bilirubin levels. Low levels of Ca 19-9 were independently associated with AIP, compared with pancreatic adenocarcinoma [odds ratio (OR) 0.28; 95 % confidence interval (CI) 0.13-0.59; p = 0.0001]. Using an upper level of 74 U/ml, the assay for Ca 19-9 identified patients with AIP with 73 % sensitivity and 74 % specificity. Using a lower level of 2.6 g/l, the assay for IgG4 identified these patients with 70 % sensitivity and 100 % specificity. Combining data, levels of Ca 19-9 < 74 U/ml and IgG4 > 1.0 g/l identified patients with AIP with 94 % sensitivity and 100 % specificity. Patients with AIP have lower levels of Ca 19-9 than those patients with pancreatic carcinoma. Measurement of either the Ca 19-9 or the IgG4 level alone are not accurate enough for diagnosis. However, the combination of Ca 19-9 < 74 U/ml and IgG4 > 1.0 g/l distinguishes patients with AIP from those patients with pancreatic carcinoma with 94 % sensitivity and 100 % specificity.