Estimating Kidney Function: Creatinine and Cystatin C

Estimates of GFR were calculated on the basis of serum creatinine, cystatin C and creatinine-cystatin C, according to the equations of the Chronic Kidney Disease Epidemiology Collaboration^{16 (link),17 (link)}. Venous blood was drawn from all study participants at the examination appointment and sent to the laboratory department of Augsburg Central Hospital within 2 to 4 h. Serum creatinine concentration were analyzed using an enzymatic colorimetric method (Dimension Vista 1500, Siemens Healthcare Diagnostics, Eschborn, Germany, or Cobas c702, Roche Diagnostics GmbH, Mannheim, Germany). Cystatin C levels were assessed using a nephelometric immunoassay (normal range 0.50–0.96 mg/L, Roche Diagnostics GmbH, Mannheim, Germany)^{18 (link),19 (link)}. Urinary albumin concentration was measured using an immunoturbidimetric assay (Tina-quant_Albumin in Urine, Boehringer Mannheim, Germany) from a single urine sample stored at − 80 °C^{19 (link)}. eGFR was calculated on the basis of the Chronic Kidney Disease Epidemiology Collaboration equation, which is based on both serum creatinine and cystatin C^{16 (link)}.