Immunoglobulin G levels can predict non-diabetic renal disease in patients with type 2 diabetes mellitus

Background: Proteinuria in patients with diabetes mellitus (DM) is sometimes caused by glomerular diseases other than diabetic nephropathy. In patients with type 2 DM (T2DM), specific predictors for non-diabetic renal disease (NDRD) are needed in addition to the traditional indicators for renal biopsy. Methods: From 1 January 2000 to 31 March 2011, we retrospectively enrolled 54 T2DM patients with proteinuria who had undergone renal biopsies into the present study. Associations between NDRD and 20 potential biomarkers, including serum levels of Igs and proteins associated with kidney function, and urinary protein and red blood cell levels, and hepatitis virus carrier status, were analyzed by multivariate logistic regression. Results: Multivariate logistic regression showed that reduced serum IgG (odds ratio [OR] 0.997; P=0.006; 95% confidence interval [CI] 0.94-0.998) and creatinine (Cr; OR 0.587; P=0.014; 95% CI 0.348-0.897) were predictors of NDRD. The area under the receiver operating characteristic curve (AUC _ROC) confirmed the good discriminatory power of IgG (AUC _ROC 0.857±0.058; 95% CI 0.744-0.970; P<0.001) and Cr (AUC _ROC 0.838±0.054; 95% CI 0.732-0.943; P<0.001). The IgG level below which the risk for NDRD increased, as calculated by obtaining the best Youden index, was 919.5mg/dL (sensitivity 91.7%; specificity 83.3%), and the corresponding Cr level was 4.1mg/dL (sensitivity 58.3%; specificity 96.7%). Conclusion: Serum IgG levels <919.5mg/dL and serum Cr levels <4.1mg/dL are associated with NDRD in T2DM patients.