[Basic and clinical studies for IgG4 measurement by nephelometric immunoassay]

After 2001, many reports have shown that serum IgG4 levels specifically elevate in patients with autoimmune pancreatitis (AIP), suggesting its clinical usefulness in discrimination between AIP and pancreatic cancer. To confirm this, we tried to examine a utility of IgG4 by measuring serum IgG4 levels of patients with healthy human, AIP, chronic pancreatitis, pancreatic cancer and autoimmune disease with nephelometric immunoassay (NIA). The between-assay variation (with coefficient of variation (CV)) in the IgG4 measurement and the within-assay variation were 0.3-3.2% and 1.9-4.5%, respectively. The analytical error was small as shown in 2.9%. Reference range of men and women was 5.6-117.2 mg/dl and 4.3-94.0 mg/dl, respectively, and men showed higher level than women significantly (p<0.05). The median IgG4 level (247.0 mg/dl) of patients with AIP showed significantly high level (p<0.01) compared with each patient group of a chronic pancreatitis (45.0 mg/dl), that of pancreatic cancer (59.6 mg/dl) and that of the autoimmune diseases (54.5 mg/dl). In discrimination between AIP and pancreatic cancer, we found excellent clinical utility showing sufficient sensibility (87.0%) and specificity (93.3%). As a result, we think the measurement of IgG4 is useful for the diagnosis of AIP. However, more popular assay system, such as immunoturbidimetry, will be needed for IgG4 measurement to be prevalent more widely.