Cystatin c immunoassay

Plasma Cystatin C was measured with a particle-enhanced turbidimetric immunoassay (Gentian cystatin C immunoassay, Gentian AS, Moss, Norway) and a Cobas® Modular P800 analyzer (Roche Diagnostics GmbH, Mannheim, Germany) that has an intra-assay CV of 1.7%, inter-assay CV was 2.8% and LOD 0.40 mg/L. The inter-assay CV for internal quality control with pooled blood donor sera was 3.2%, Equalis AB (www.equalis.se) provided the external quality control.

The presence of potassium, sodium, urea, and creatinine in urine samples was determined with a MEGA clinical chemistry analyzer (Merck). Potassium, and sodium were determined by indirect potentiometry, and urea was determined by a photometric test with the urease-GIDH method. Estimated glomerular filtration rate (eGFR) was calculated based on the combined creatinine and cystatin C Chronic Kidney Disease-Epidemiology Collaboration equation (12 ). Serum and urinary creatinine, plasma total cholesterol, and triglycerides were determined from fasting blood samples by using Kodak Ektachem dry chemistry (Eastman Kodak). Plasma HDL cholesterol was measured with a homogeneous method (direct HDL, Aeroset TM System, Abbott Laboratories). Plasma renin concentration was measured using an automated sandwich immunochemiluminescent assay (LIAISON®, Diasorin). Serum aldosterone concentration was measured using a competition-based radioimmunoassay (ALDOCTK-2, Diasorin). Serum cystatin C concentrations were measured by a Gentian Cystatin C Immunoassay (Gentian AS) on a modular analyzer (Roche Diagnostics). Urinary albumin concentration was determined by nephelometry (Dade Behring Diagnostic). Urinary albumin-to-creatinine ratio (ACR) was calculated by dividing the urinary albumin concentration (mg/L) by the urinary creatinine concentration (mmol/L).