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

Background: 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. Methods: 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. Results: 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. Conclusions: 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.

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