Cystatin C as a filtration marker – haemodialysis patients expose its strengths and limitations

Objective. The reliability of serum cystatin C (s‐Cys) as a filtration marker depends on the intra‐ and inter‐individual variation and influence of non‐renal factors of its production rate (Cyspr), non‐renal clearance (CLnr) and sieving coefficient (S). Haemodialysis patients with no residual renal function would be the best population in which to investigate these variables, which otherwise require reliable GFR measurements. Material and methods. Seventy‐nine haemodialysis (HD) patients with negligible residual renal function (Group 1) were investigated and compared with 55 HD patients with varying degrees of residual renal function (Group 2) and 923 non‐dialysis patients (Group 3). The equation eGFR = Cyspr/s‐Cys−CLnr was used to analyse the turnover and variation of cystatin C. Results. A formula for estimating GFR, eGFR = 99/s‐Cys−14.1, calculated from Group 3, was shown to fit the HD patients. The measured s‐Cys in Group 1 was 6.9±0.9 and 6.4±1.1 mg/L in Group 2. The calculated 95 % confidence interv...