Estimation of glomerular filtration rate in obese patients with chronic renal impairment based on serum cystatin C levels

Background: Serum cystatin C (S-cyst) has an obvious advantage in recognizing the initial stages of renal impairment. However, several recent studies suggest that S-cyst may also be affected by some non-glomerular 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 S-cyst. Patients and methods: The study was performed in 33 patients (mean age 49.1 +/- 6.3 years) with chronic renal disease (S-cr = 227 +/- 118 mumol/l) and BMI = 35.6 +/- 1.8 kg/m(2), and in 78 patients (mean age 43.4 +/- 5.1 years) with chronic renal disease (S-cr = 245 111 mumol/l) and BMI = 24.0 +/- 1.8 kg/m(2). Glomerular filtration rate (GFR) was determined using renal inulin clearance (C-in) under conditions of stabilized plasma concentrations and water loading. S-cyst 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 1/S-cyst and C-in was demonstrated in patients with BMI >= 30 kg/m(2) (Group A). Similarly, a significant correlation (r = 0.900, p < 0.001) between 1/S-cyst and C-in was found in patients with BMI < 30 kg/m(2) (Group B). There was no significant difference between the regression straight lines characterizing these relationships. ROC curve analysis (using a cut-off value for C-in = 30 ml/min/1.73 m(2)) did not show significant differences in AUC, sensitivity and specificity for S-cyst between obese and nonobese patients. Conclusion: The results suggest that evaluation of GFR based on S-cyst in obese patients need not differ from that in nonobese ones.