Creatinine-based and cystatin C-based GFR estimating equations and their non-GFR determinants in kidney transplant recipients

Background and objectives eGFR equations have been evaluated in kidney transplant recipients with variable performance.We assessed the performance of the Modification ofDiet in Renal Disease equation and the Chronic Kidney Disease Epidemiology Collaboration equations on the basis of creatinine, cystatin C, and both (eGFR creatinine-cystatin C) compared with measured GFR by iothalamate clearance and evaluated their non-GFR determinants and associations across 15 cardiovascular risk factors. Design, setting, participants, & measurements A cross-sectional cohort of 1139 kidney transplant recipients >1 year after transplant was analyzed. eGFR bias, precision, and accuracy (percentage of estimates within 30% of measured GFR)were assessed. Interaction of each cardiovascular risk factorwith eGFR relative tomeasured GFR was determined. Results Median measured GFR was 55.0 ml/min per 1.73 m². eGFR creatinine overestimated measured GFR by 3.1% (percentage of estimates within 30% of measured GFR of 80.4%), and eGFR Modification of Diet in Renal Disease underestimated measured GFR by 2.2%(percentage of estimateswithin 30%ofmeasured GFR of 80.4%). eGFR cystatin C underestimated measured GFR by 213.7% (percentage of estimates within 30% of measured GFR of 77.1%), and eGFR creatinine-cystatinCunderestimatedmeasuredGFR by28.1% (percentage of estimates within 30%ofmeasured GFR of 86.5%). Lower measured GFR associatedwith older age,women, obesity, longer time after transplant, lower HDL, lower hemoglobin, lower albumin, higher triglycerides, higher proteinuria, and an elevated cardiac troponin T level but did not associate with diabetes, smoking, cardiovascular events, pretransplant dialysis, or hemoglobin A1c. These risk factor associations differed for five risk factors with eGFR creatinine, six risk factors for eGFR Modification ofDiet in Renal Disease, ten risk factors for eGFR cystatin C, and four risk factors for eGFR creatinine-cystatin C. Conclusions Thus, eGFR creatinine and eGFR creatinine-cystatin C are preferred over eGFR cystatin C in kidney transplant recipients because they are less biased, more accurate, and more consistently reflect the same risk factor associations seen with measured GFR.