Background: Serum cystatin C (Scyst) has an obvious advantage in recognizing the initial stages of renal impairment. However, several recent studies suggest that Scyst may also be affected by some nonglomerular factors such as thyroid dysfunction, glucocorticoid administration or metabolic status of the diabetic patient. The aim of this study was to evaluate whether obesity could affect Scyst.
Patients and methods: The study was performed in 33 patients (mean age 49.1 +/- 6.3 years) with chronic renal disease (Scr = 227 +/- 118 micromol/l) and BMI = 35.6 +/- 1.8 kg/m2, and in 78 patients (mean age 43.4 +/- 5.1 years) with chronic renal disease (Scr = 245 +/- 111 micromol/l) and BMI = 24.0 +/- 1.8 kg/m2. Glomerular filtration rate (GFR) was determined using renal inulin clearance (Cin) under conditions of stabilized plasma concentrations and water loading. Scyst was measured using immunonephelometry. For statistical evaluation, linear regression analysis and receiver-operating characteristic (ROC) curve analysis were used.
Results: A significant correlation (r = 0.956, p < 0.001) between l/Scyst and Cin was demonstrated in patients with BMI > or = 30 kg/m2 (Group A). Similarly, a significant correlation (r = 0.900, p < 0.001) between l/Scys and Cin was found in patients with BMI < 30 kg/m2 (Group B). There was no significant difference between the regression straight lines characterizing these relationships. ROC curve analysis (using a cut-off value for Cin = 30 ml/min/1.73 m2) did not show significant differences in AUC, sensitivity and specificity for Scyst between obese and nonobese patients.
Conclusion: The results suggest that evaluation of GFR based on Scyst in obese patients need not differ from that in nonobese ones.