Estimating GFR in Renal Transplanted Patients With Equations Based on Creatinine (With or Without Race Variable) and/or Cystatin C

Abstract

BACKGROUND AND AIMS
Current Glomerular filtration rate (GFR) estimating equations based on serum creatinine are facing increased criticism due to the inclusion of a race correction in black Americans with the CKD-EPI equation (CKD-EPIASR, A = Age, S = Sex, R = Race). New equations without race (CKD-EPIAS) has been proposed with creatinine and/or cystatin C. These equations were developed mainly from US cohorts with few renal transplanted patients. In the current analysis, we compared these new equations, notably with the new European Kidney Function Consortium (EKFC) equation.

METHOD
In this retrospective analysis, 489 transplanted patients from the University Hospital of Saint-Etienne were included. All subjects were white. GFR was measured with inulin or iohexol clearances. IDMS creatinine and standardized cystatin C results were available. Median bias (eGFR—mGFR), imprecision (interquartile range: IQR), and P30 accuracy (percentage of eGFR-values within ± 30% of mGFR) were calculated.

RESULTS
Among creatinine-based equations, the bias were 2.3, 5.5 and 2.2 mL/min/1.73 m² for the CKD-EPIASR, CKD-EPIAS and EKFC, respectively. IQRs were 16.1, 16.2 and 15.3 mL/min/1.73 m², respectively. P30 were 74.2, 68.3 and 75.3%, respectively. Among cystatin C-based equations, the bias were −3.1 and 0.8 mL/min/1.73 m² for the CKD-EPICC and the EKFCCC, respectively. IQRs were 13.7 and 13.4 mL/min/1.73 m², respectively. P30 were 78.5 and 81.4%, respectively. Among equations combining creatinine and CC, the bias were −1.3, 0.5 and 1.6 mL/min/1.73 m² for the CKD-EPIASR-CC, CKD-EPIAS-CC and EKFCcreatCC, respectively. IQRs were 12.7, 12.4 and 12.1 mL/min/1.73 m², respectively. P30 were 84.5, 82.6 and 80.6%, respectively.

CONCLUSION
In our cohort of European transplanted patients, both the EKFCcreat and CKD-EPIASR equations performed better than the new CKD_EPIAS. Compared with creatinine-based equations, the new EKFCCC equation and all combined equations performed better. Cystatin C-based equations have the advantage to be accurate without any race variable.