Poor positive predictive value of serum immunoglobulin G4 concentrations in the diagnosis of immunoglobulin G4-related sclerosing disease

BACKGROUND Immunoglobulin G4 (IgG4)-related sclerosing disease is a recently described clinicopathological entity with diverse manifestations including, amongst others, autoimmune pancreatitis, sclerosing cholangitis, sclerosing sialadenitis and retroperitoneal fibrosis. Elevated serum IgG4 concentration has been described as the hallmark of this condition with reported good sensitivity and specificity. OBJECTIVE We sought to establish the utility of serum IgG4 concentrations in the diagnosis of IgG4-related sclerosing disease by determining how many serum samples with elevated IgG4 from an unselected population would originate from patients who fulfilled criteria for this diagnosis. METHODS The clinical features and laboratory characteristics of patients whose serum IgG4 concentration was greater than 1.30 g/L were analysed retrospectively from a total of 1,258 IgG subclass measurements performed in a tertiary hospital diagnostic laboratory. RESULTS Eighty patients (6.4%) had elevated IgG4 concentrations greater than 1.30 g/L. Nine of 61 patients had the diagnosis of IgG4-related sclerosing disease, giving a poor positive predictive value of 15%. The median serum IgG4 concentrations of those with and without IgG4-related sclerosing disease were 2.16 g/L and 1.86 g/L, respectively (p = 0.22). CONCLUSION Serum IgG4 concentration has poor positive predictive value in the diagnosis of IgG4-related sclerosing disease and, therefore, the clinical significance of elevated serum IgG4 concentration alone must be interpreted with caution.