Proteinuria and outcome after renal transplantation: ratios or fractions?

Proteinuria is associated with poorer outcomes in renal transplant recipients. Fractional excretion of total protein (FEPR) may better reflect kidney damage than urine protein-to-creatinine ratio (PCR).

We assessed FEPR (FEPR = [serum creatinine × urine protein] / [serum protein × urine creatinine], %) and PCR ([urinary protein/urinary creatinine] × 1000, mg/mM) 1 year after first renal transplantation as predictors of transplant failure. The primary endpoints were transplant failure and death. The use of the tests was analyzed by constructing receiver operator characteristic curves and comparing the area under the curve. Using receiver operator characteristic analysis, patients were stratified into high- and low-risk groups.

Two hundred nineteen recipients were followed up for a median of 4.9 years. At a median of 2.7 years, 11.4% (n=25) of the transplants failed. Eight percent (n=17) of the patients died. The area under the curve was higher for FEPR than PCR (0.92 vs. 0.84). Patients with an FEPR of 0.019% or higher had a 3.4-fold (P=0.003) increased risk of transplant failure and a 2.3-fold (P=0.02) increased risk of death compared with those with an FEPR of less than 0.019%. Patients with a PCR of 97 mg/mM or greater had a 2.1-fold (P=0.04) increased risk of transplant failure and a 1.6-fold (P=0.04) increased risk of death compared with those with a PCR of less than 97 mg/mM (P=0.04). In multivariate analysis with time to transplant failure as the dependent variable, FEPR and PCR were independent predictors of transplant failure (hazards ratio, 1.07 [P=0.013] and 1.03 [P=0.03], respectively).

FEPR and PCR at 1 year are independent predictors of transplant failure, but FEPR may be superior.