Increase diagnostic accuracy in differentiating focal type autoimmune pancreatitis from pancreatic cancer with combined serum IgG4 and CA19-9 levels.

BACKGROUND/OBJECTIVES: To distinguish autoimmune pancreatitis (AIP), especially focal type, from pancreatic cancer, is a greatest challenge for clinician. The aim of the study is to compare the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of combined serum IgG4 and CA19-9 levels to differentiate AIP from pancreatic cancer by HISORt, Asian and international consensus diagnostic criteria.

METHODS: We measured serum IgG4, CEA, and CA19-9 levels in 188 AIP patients, 86 non-AIP chronic pancreatitis patients, and 130 pancreatic cancer patients. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy were compared with different diagnostic criteria. We also compared the diagnostic performance in patients with or without jaundice.

RESULTS: The serum level of IgG4 was significantly higher in AIP than those in non-AIP chronic pancreatitis and pancreatic cancer. The optimal cutoffs of IgG4 and CA19-9 to differentiate AIP from pancreatic cancer were 175 mg/dL and 85.0 U/ml based on ROC analysis. Combining IgG4 level over 280 mg/dL and CA19-9 below 85.0 U/ml could yield a best diagnostic accuracy (85.6%) to distinguishing AIP from pancreatic cancer in all of the HISORt, Asian and international consensus diagnostic criteria. With the combination of serological test, focal type AIP could be diagnosed with comparable accuracy as diffuse type AIP.

CONCLUSIONS: Our study demonstrated that combined use of serum IgG4 (over 280 mg/dL) and CA19-9 9 (below 85.0 U/ml) together increases the diagnostic accuracy to distinguish AIP from pancreatic cancer non-invasively, especially in focal type autoimmune pancreatitis.