Serum immunoglobulin G4 level is a poor predictor of immunoglobulin G4-related disease.

OBJECTIVES: 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.