Clinical usefulness of serum cystatin C and the pertinent estimation of glomerular filtration rate based on cystatin C

Abstract

Aim: Although cystatin C has been developed as an alternative marker for estimating glomerular filtration rate (GFR), its clinical use is as yet limited. The significance of cystatin C for differentiating chronic kidney disease (CKD) stages and established cystatin C-based equations estimating GFR were evaluated. Methods: The fresh frozen serum samples from CKD (n = 119) and healthy volunteers (n = 22) were evaluated. Serum creatinine (sCr) was measured by the kinetic Jaffe method, and recalibrated to the isotope dilution mass spectrometry (IDMS). Cystatin C was measured using a particle-enhanced nephelometric assay. Results: CKD stages were more sensitively differentiated by cystatin C compared to sCr, especially in moderate and severe kidney dysfunction. Sex and body mass index did not affect cystatin C level. Pearson`s correlation coefficients of reciprocal of cystatin C, measured and recalibrated sCr compared to systemic inulin clearance (Cl(in)) were 0.757, 0.734 and 0.709, respectively. We derived novel pertinent equations based on cystatin C (model 1: 1.404 x cystatin C-0.895 x age0.006 x weight1.074 x height-1.562 x (0.865; if female); model 2: 43.287 x cystatin C-0.906 x age0.101 x (0.762; if female)]. Models 1 and 2 showed superior performance in representing systemic Cl(in) than the IDMS Modification of Diet in Renal Disease (MDRD) study equations did (adjusted r2 = 0.76 and 0.72 for models 1 and 2, and 0.64 and 0.65 for 4 and 6 variable IDMS MDRD equations, respectively). Conclusion: Cystatin C reflects kidney dysfunction sensitively, and thus cystatin C-based estimation of GFR could provide a reliable support for clinical practice.