GFR estimates incorporating cystatin C (CysC) and creatinine (Cr) have shown to perform better than Cr only in subjects with reduced GFR but have not been studied in kidney transplant recipients (KTR).

We analyzed the cross-sectional and longitudinal performance of newly developed Chronic Kidney Disease Epidemiology Collaboration (CKD- EPI) equations using cysC alone (CKD-EPI CysC), Cr alone (CKD-EPI Cr), or both: CKD-EPI (Cr-CysC), and the Modification of Diet in Renal Disease (MDRD) formula against iohexol GFR in 153 KTR enrolled in Angiotensin II Blockade for Chronic Allograft Nephropathy Trial (NCT 01467895). Iohexol GFR was measured at baseline (1 month post transplant), 1 year, and yearly thereafter up to 5 years.

Results:

Mean mGFR, Cr and CysC at baseline were 56.1 ±17.0 mL/min/1.73 m², 1.2 mg/dL, and 1.3 mg/L, respectively. Performance of formulas against iohexol GFR is shown in table 1. Bias was the largest for CKD-EPI Cr and comparable among other equations. eGFR MDRD and CKD-EPI (Cr-CysC) were the most accurate. Precision was vastly the best for CKD-EPI (Cr-CysC) formula.

The 5 year iohexol GFR was 53.8± 16.8 ml/min/1.73m². eGFR CKD-EPI(Cr-CysC) had the lowest variability with respect to its bias (Figure1) and the slope was not significantly different from iohexol GFR (p=0.113).

Conclusion:

CKD-EPI (Cr-CysC) eGFR is superior to formulas utilizing either marker alone for estimating GFR in KTR and should be employed to estimate GFR in cross sectional and longitudinal assessment of kidney function in situations where more precise GFR estimation is necessary.

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