Copyright @ Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. The Sensitivity and Specificity of Serum Immunoglobulin G and Immunoglobulin G4 Levels in the Diagnosis of Autoimmune Chronic Pancreatitis Korean Experience Eun Kwang Choi, MD,* Myung-Hwan Kim, MD, PhD,Þ Tae Yoon Lee, MD,Þ Seunghyun Kwon, MD,Þ Hyoung-Chul Oh, MD,Þ Chang Yun Hwang, MD,Þ Dong Wan Seo, MD, PhD,Þ Sang Soo Lee, MD, PhD,Þ and Sung Koo Lee, MD, PhDÞ Objectives: Serum immunoglobulin G (IgG) and/or IgG4 elevation is one of the notable characteristics of autoimmune chronic pancre- atitis (AIP). The purpose of this study was to compare the sensitivity and specificity of IgG with those of IgG4 in the diagnosis of AIP. Methods: From December 2005 to March 2006, patients who were diagnosed as having ordinary chronic pancreatitis of a certain cause (n = 67) and pancreatic cancer (n = 76) in Asan Medical Center were enrolled. The IgG and IgG4 levels of these patients were compared with those of 35 AIP patients diagnosed in Asan Medical Center. Results: The percentage of patients with serum IgG level more than 1800 mg/dL was 10.4% (7/67), 2.6% (2/76), and 54.3% (19/35) in patients with ordinary chronic pancreatitis, pancreatic cancer, and AIP, respectively. As for serum IgG4 levels more than 135 mg/dL, it was 11.9% (8/67), 1.3% (1/76), and 73.3% (22/30), respectively. The specificity of IgG at 1800 mg/dL and IgG4 at 135 mg/dL was both 93.7%. The serum IgG4 showed high specificity (98.7%) in differentiating AIP from pancreatic cancer. The IgG4 level at 141 mg/dL was determined as the most optimal cutoff value with resulting sensitivity and specificity of 73.3% and 95.1%, respec- tively (area under the curve, 0.816), whereas for IgG, it was determined as 1770 mg/dL, with sensitivity and specificity of 57.1% and 93.7% (area under the curve, 0.788). Conclusions: The sensitivity of serum IgG4 tended to be higher than that of IgG in the diagnosis of AIP. The IgG4 showed high spe- cificity in the differential diagnosis of AIP from pancreatic cancer. Serum IgG4 should be included in the diagnostic workup for AIP. Key Words: autoimmune pancreatitis, pancreatic cancer, IgG, IgG4 (Pancreas 2007;35:158Y163) A utoimmune chronic pancreatitis (AIP) can be defined as a chronic inflammation of the pancreas caused by an autoimmune mechanism; autoimmunity is responsible for producing the pancreatic lesion. 1,2 The AIP is a distinctive type of chronic pancreatitis that shows reversibility of pancreatic morphology and function with oral steroid therapy in contrast to ordinary chronic pancreatitis. 1Y5 Abnormally elevated levels of serum gamma globulin and/or immunoglobulin G (IgG) or the presence of auto- antibodies are the laboratory criterion of AIP proposed by the Japan Pancreas Society. 6 In English literature, however, there are few reports comparing the diagnostic sensitivities of IgG and IgG4 for AIP. Moreover, there are only few reports 7 that showed the usefulness of serum IgG and IgG4 in distinguish- ing AIP from pancreatic cancer and ordinary chronic pancreatitis until now. The IgG4 level is used by some groups in the diagnosis of AIP, and although not included in the former Japanese diagnostic criteria, it has been included in the revised Japanese proposal recently (Table 1). 8Y10 On the contrary, the Italian group does not use IgG4 in the diagnosis of AIP because they believe IgG4 is not very specific for AIP. 11 In addition, the optimal cutoff value of IgG and IgG4 has not been agreed upon among different authors. For these reasons, we measured serum IgG and IgG4 levels in patients with AIP and other pancreatic diseases (ordinary chronic pancreatitis and pancreatic cancer) to investigate the diagnostic sensitivity and specificity and to find out the most optimal cutoff value of IgG and IgG4 using receiver operating characteristic (ROC) curve. MATERIAL AND METHODS Patients The enrolled AIP patients were diagnosed as having AIP in our institution during the past 4 years. As the comparison group, we enrolled patients who were diagnosed as having ordinary chronic pancreatitis with a certain cause other than AIP and pancreatic cancer from December 2005 to March 2006. All patients with ordinary chronic pancreatitis had both marked irregular dilatation of the main pancreatic duct or dominant dorsal duct and multiple calcification or ORIGINAL ARTICLE 158 Pancreas & Volume 35, Number 2, August 2007 Received for publication August 18, 2006; accepted February 27, 2007. From the *Department of Internal Medicine, Cheju National University College of Medicine, Jeju; and †Department of Internal Medicine, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea. Reprints: Myung-Hwan Kim, MD, PhD, Department of Internal Medicine, University of Ulsan College of Medicine, Asan Medical Center, 388-1 Pungnap-dong, Songpa-gu, Seoul 138-736, Korea (e-mail: mhkim@amc. seoul.kr). Copyright * 2007 by Lippincott Williams & Wilkins