β2-Microglobulin and Cystatin C in Type 2 Diabetes: Assessment of Diabetic Nephropathy

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Abstract
Background: Changes in glomerular filtration rate (GFR) provide a valuable indicator of the progression of diabetic nephropathy (DN). This study was designed to demonstrate the clinical values of serum cystatin C (Cys C) and β2-microglobulin in the assessment of renal function in type 2 diabetics by comparing them with the GFR, estimated from the uptake phase of 99 m technetium dimetiltriamino pentaacetic acid renogram (GFR-DTPA) and creatinine clearances. Materials and Methods: 68 type 2 diabetic patients with (urinary albumin excretions (UAE) 30 - 300 mg/24 h) (n = 39) and without (UAE < 30 mg/24 h) (n = 29) microalbuminuria and 32 controls were enrolled in the study. Serum Cys C, β2-microglobulin, creatinine, urinary microalbumin levels, creatinine clearances and GFR-DTPA values were determined in all groups. Non-parametric ROC curves, using a cut-off GFR-DTPA of 60 mL/min/1.73 m2, were obtained for these markers. Results: Serum Cys C, β2-microglobulin, glucose and HbA1c concentrations were significantly higher in the group with diabetes compared to controls. In the patients with microalbuminuria, serum Cys C and glucose concentrations increased significantly in comparison to patients with normoalbuminuria, while no differences were observed for β2-microglobulin levels. Serum creatinine concentrations, GFR-DTPA values and creatinine clearances were not different between both diabetic groups and controls. Cys C was positively correlated with β2-microglobulin and creatinine and negatively with GFR values; β2-microglobulin was also positively correlated with serum creatinine in microalbuminurics. A significant inverse correlation was found between β2-microglobulin and GFR values in both microalbuminurics and normoalbuminurics. Conclusions: Increased Cys C and β2-microglobulin in diabetics may be early indicators of incipient DN. The diagnostic accuracies of Cys C and β2-microglobulin are superior to that of serum creatinine in distinguishing between mild and moderately reduced GFR.