Study of cystatin C (Cys C) in relation to the calculation of the glomerular filtration rate and bioelectrical impedance analysis parameters in obese patients with and without type 2 diabetes

Introduction

Assessment of renal function based on quantification of the glomerular filtration rate (GFR) is essential for early detection of damage and progression of renal diseases. The purpose of our study was to determine the value of cystatin C (Cys C) assays in the calculation of the GFR and bioelectrical impedance analysis parameters in obese subjects aged 30-70 years with moderately damaged renal function.

Materials and methods

Cys C levels were measured with a new immunoturbidimetric kit (Roche Diagnostics) and an automated Cobas c6000 analyzer. In the GFR calculation, creatinine and Cys C levels were included. The GFR calculated with the equation that included Cys C in obese and normal-weight patients is not affected by changes in the lean body mass.

Results

Obese patients (N=70) had a mean (± SD) serum creatinine level of 1.52±1.0 mg/dL and a mean Cys C level of 1.28±0.59 mg/L. In this group, the GFR calculated on the basis of MDRD, Cys C, and creatinine clearance values showed similar filtered values between MDRD and Cys C and a DS value smaller in the case of Cys C. The correlation (R²) between GFR and its metabolite is higher in the case of Cys C when somatotype parameters (measured with bioelectrical impedance analysis) were introduced into the equation.

Conclusions

When Cys C is included in calculations of GFR, the result shows a higher correlation degree compared to the MDRD system. Given that Cys C shows less intra-individual variability than creatinine, it can be applied in routine diagnostics in a larger number of patients.