title: The combined measurement of total serum IgG and IgG4 may increase diagnostic sensitivity for autoimmune pancreatitis without sacrificing specificity, compared with IgG4 alone.
abstract: OBJECTIVE
  Until now, there was no international consensus on the diagnostic criteria for autoimmune pancreatitis (AIP). As for serologic criteria, the HISORt criteria use elevated immunoglobulin (Ig) G4 alone, whereas the Asian diagnostic criteria include elevations of total IgG or IgG4, or the presence of autoantibodies. This study was mainly aimed at determining whether the combined measurement of total IgG and IgG4 could increase the diagnostic sensitivity for AIP while maintaining specificity, compared with IgG4 alone. Another aim was to determine the utility of autoantibodies to diagnose AIP.
  
  
  METHODS
  We prospectively measured total serum IgG and IgG4 together in 82 consecutive patients with AIP, and seropositivity was defined as elevation of either total IgG or IgG4. To evaluate specificity in the differentiation of AIP from pancreatic cancer, total serum IgG and IgG4 were prospectively measured in 110 patients with pancreatic cancer. Also, the detection rates of antinuclear antibody (ANA) and rheumatoid factor (RF) were retrospectively reviewed in patients with AIP.
  
  
  RESULTS
  In patients with AIP, the sensitivity of IgG4 (> or = 135 mg/dl) was 52.5% (43/82), significantly higher than that (46.3%, 38/82) of total IgG (> or = 1,800 mg/dl) (P<0.05). The sensitivity of combined measurement of total IgG and IgG4 for AIP was 68.3% (56/82), significantly higher than that of IgG4 alone (P<0.05). The specificity of total IgG and IgG4 in the differentiation of AIP from pancreatic cancer was 96.4 and 99.1%, respectively. The specificity of combined measurement of total IgG and IgG4 was 95.5%, and it was not significantly different from that of IgG4 alone (P=0.125). The sensitivity of ANA (> or = 1:80) and RF was 24.4% (19/78) and 20.3% (13/64), respectively. All but one patient who had positive results for ANA or RF also showed elevations of either total IgG or IgG4, respectively.
  
  
  CONCLUSIONS
  The combined measurement of total serum IgG and IgG4 may increase diagnostic sensitivity without sacrificing specificity, compared with IgG4 alone. However, the measurement of ANA or RF may show no additional benefit when combined with total serum IgG and IgG4.
authors.affiliation: Department of Gastroenterology, Asan Medical Center, Internal Medicine, University of Ulsan College of Medicine, 388 - 1 Pungnap-dong, Songpa-gu, Seoul 138-736, Korea.
authors.forename: Tae Jun
authors.initials: TJ
authors.lastname: Song
authors.forename: Myung-Hwan
authors.initials: MH
authors.lastname: Kim
authors.forename: Sung-Hoon
authors.initials: SH
authors.lastname: Moon
authors.forename: Jun Bum
authors.initials: JB
authors.lastname: Eum
authors.forename: Do Hyun
authors.initials: DH
authors.lastname: Park
authors.forename: Sang Soo
authors.initials: SS
authors.lastname: Lee
authors.forename: Dong Wan
authors.initials: DW
authors.lastname: Seo
authors.forename: Sung Koo
authors.initials: SK
authors.lastname: Lee
mesh_terms: D000974:Antibodies, Antinuclear / Q000097:blood; D001327:Autoimmune Diseases / Q000097:blood / Q000175:diagnosis*; D015415:Biomarkers / Q000097:blood; D016009:Chi-Square Distribution; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D008297:Male; D008875:Middle Aged; D010190:Pancreatic Neoplasms / Q000097:blood; D050500:Pancreatitis, Chronic / Q000097:blood / Q000175:diagnosis*; D011446:Prospective Studies; D012217:Rheumatoid Factor / Q000097:blood; D012680:Sensitivity and Specificity
chemical_list: D000974:Antibodies, Antinuclear; D015415:Biomarkers; D007074:Immunoglobulin G; D012217:Rheumatoid Factor