Serum levels of immunoglobulin G and complement 3 differentiate non-diabetic renal disease from diabetic nephropathy in patients with type 2 diabetes mellitus.

AIMS: Heavy proteinuria caused by non-diabetic renal disease (NDRD) is common in type 2 diabetes mellitus (T2DM). The aim of this study was to investigate specific predictors for NDRD in addition to traditional indicators in T2DM.

METHODS: A total of 341 patients with T2DM who underwent renal biopsy were retrospectively included. Eligible patients were divided into a nephrotic-range group (n = 194) and a non-nephrotic-range group (n = 147) based on proteinuria level. Risk factors for NDRD were evaluated using logistic regression, and the diagnostic implications of these variables were assessed by subgroup.

RESULTS: Multivariate logistic regression indicated that serum IgG level (OR, 0.762; 95% CI, 0.628-0.924; p = 0.006) was an independent predictor of NDRD in the nephrotic-range group. However, in the non-nephrotic-range group, increased C3 level was an independent risk factor for NDRD (OR, 1.313; 95% CI, 1.028-1.678; p = 0.029). In the nephrotic-range group, the optimal cutoff value of IgG for predicting NDRD was 734.0 mg/dl, with 67.8% sensitivity and 74.8% specificity, and IgG ≤ 734.0 mg/dl was the best predictor of NDRD. In the non-nephrotic-range group, the optimal cutoff value of C3 for predicting NDRD was 122.0 mg/dl with low sensitivity (30.9%) but high specificity (97.8%).

CONCLUSIONS: At different levels of proteinuria, reduced IgG and increased C3 levels were independent indicators of NDRD in T2DM. Insights into these factors will help to advance the clinical management of NDRD.