In renal transplantation, death with a functioning graft remains one of the main causes of graft loss. In the general population, renal function impairment is strongly associated with cardiovascular and all cause mortality. Whether this association holds true for kidney transplant recipients (KTR) is unclear. This uncertainty is likely to be due, in part, to the fact that glomerular filtration rate (GFR) estimation based on serum creatinine (SCr) does not always provide an accurate evaluation of the graft function in KTR. As compared to SCr, we have recently shown in a large cohort of KTR that serum cystatin C (SCysC) is a much better marker of GFR.

Herein, we sought to study the ability of the 1-year-post-transplant renal function to predict all cause mortality according to the methods used to assess GFR.

Three hundred and forty two consecutive KTR for whom a measurement of GFR by inulin clearance was available at 1 year post-transplant were included. SCr and ScysC were measured with standardised methods. The association of the 1-year inulin clearance value the 1-year MDRD Study equation value and the 1-year CKD-EPI ScysC equation value with all cause mortality was studied by ROC analysis and Cox model.

During a median follow-up of 145 months, 70 KTR died. Mean (±SD) inulin clearance at 1-year-post-transplant was 46 (±19) mL/min/1.73m2. Aeras under the ROC curves were similar for inulin and CKD-EPI ScysC equation values (0.564 and 0.550, respectively, NS), and were both significantly superior to that of the MDRD equation (0.483, p<0.01). In Cox analysis, while all types of GFR evaluations were significantly associated to graft loss, only an inulin and a CKD-EPI ScysC equation values below 45 mL/min/1.73m2 were associated with an excess risk of mortality (HR of 1.85 vs 1.01 for both inulin and CKD-EPI ScysC vs MDRD, respectively).

We conclude that ScysC-based GFR estimation might better predict KTR outcome as compared to a traditional SCr-based estimation. The one year-post transplant GFR value given by the CKD-EPI ScysC equation should be further evaluated as a potential surrogate marker for both graft and patient survival.

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