Cystatin C-based calculation of glomerular filtration rate in kidney transplant recipients

Cystatin C (Cys C) has been shown to be an alternative marker of renal function. However, estimation of the glomerular filtration rate (GFR) based on Cys C has received little attention. Recently, several Cys C-based equations were developed in different patient cohorts. To date, the benefit of a Cys C-based GFR calculation in patients after renal transplantation (RTx) remains to be elucidated. We compared the diagnostic accuracy of three Cys C-based formulae (Larsson, Hoek, Filler which used an immunonephelometric method) with the results of the Modification of Diet in Renal Disease (MDRD) formula. GFR was measured by means of technetium-diethylenetriamine pentaacetic acid (99mTc-DTPA) clearance in 108 consecutive patients after RTx. Correlation coefficients of all calculated GFR estimates with the true GFR were high but did not differ significantly from one another (0.83–0.87). The MDRD and Filler equations overestimated GFR significantly, whereas the Larsson equation significantly underestimated GFR. Bias of the Hoek formula was negligible. Precision of the Hoek (8.9 ml/min/1.73 m2) and Larsson equations (9.6 ml/min/1.73 m2) were significantly better than MDRD equations (11.4 ml/min/1.73 m2; P≤0.035 each). Accuracy within 30% of real GFR was 67.0 and 65.1% for the MDRD and Filler formulae, and 77.1% for the Larsson and Hoek formulae, respectively. Accuracy within 50% of true GFR for the Hoek formula (97.2%) was better than for the MDRD equations (85.3%). Cys C-based formulae may provide a better diagnostic performance than creatinine-based equations in GFR calculation after RTx.