title: Serum immunoglobulin G4 level is a poor predictor of immunoglobulin G4-related disease.
abstract: OBJECTIVE
  Immunoglobulin G4-related disease (IgG4-RD) is characterized by elevation in serum IgG4 levels, typical multiorgan involvement and dramatic response to steroid therapy. We determined the predictive value of an elevated serum IgG4 for the diagnosis of IgG4-RD. We also sought to identify novel conditions, which have characteristic features of IgG4-RD.
  
  
  METHODS
  We identified all Mayo Clinic Rochester patients with serum IgG4 levels measured between January 2008 and December 2011 (n = 6014). Those with elevated serum IgG4 levels (reference range, 121-140 mg/dL) were included in the analysis and were classified as "definite," "probable," or "no" IgG4-RD.
  
  
  RESULTS
  Serum IgG4 levels were elevated in 390 subjects (6.5%) of whom only 39 (10%) had IgG4-RD (29 "definite," 10 "probable"). The positive predictive value of an elevated serum IgG4 for IgG4-RD was poor (10%). Subjects with IgG4-RD differed from those without IgG4-RD in mean age (59.6 ± 15.2 vs 54.4 ± 18.3 years, P < 0.05), % males (90% vs 58%, P < 0.05), mean serum IgG4 level (437 ± 471 vs 223 ± 194 mg/dL, P < 0.05), and presence of chronic rhinosinusitis (7/39 vs 29/351, P = 0.05).
  
  
  CONCLUSIONS
  Elevated serum IgG4 levels are not specific for IgG4-RD and are likely to be a false-positive. Chronic rhinosinusitis is likely an as yet underrecognized manifestation of IgG4-RD.
authors.affiliation: From the Divisions of *Internal Medicine, †Gastroenterology and Hepatology, and ‡Laboratory Medicine, Mayo Clinic, Rochester, MN.
authors.forename: Taiwo N
authors.initials: TN
authors.lastname: Ngwa
authors.forename: Ryan
authors.initials: R
authors.lastname: Law
authors.forename: David
authors.initials: D
authors.lastname: Murray
authors.forename: Suresh T
authors.initials: ST
authors.lastname: Chari
mesh_terms: D000328:Adult; D000368:Aged; D001327:Autoimmune Diseases / Q000097:blood / Q000175:diagnosis; D015209:Cholangitis, Sclerosing / Q000097:blood / Q000175:diagnosis; D002908:Chronic Disease; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood*; D008297:Male; D008875:Middle Aged; D016727:Orbital Pseudotumor / Q000097:blood / Q000175:diagnosis; D010195:Pancreatitis / Q000097:blood / Q000175:diagnosis; D011237:Predictive Value of Tests; D011379:Prognosis; D012185:Retroperitoneal Fibrosis / Q000097:blood / Q000175:diagnosis; D012220:Rhinitis / Q000097:blood / Q000175:diagnosis; D012793:Sialadenitis / Q000097:blood / Q000175:diagnosis; D012852:Sinusitis / Q000097:blood / Q000175:diagnosis
chemical_list: D007074:Immunoglobulin G