Performance of cystatin C- and creatinine-based estimated glomerular filtration rate equations depends on patient characteristics

BACKGROUND: The Kidney Disease Improving Global Outcomes (KDIGO) guideline recommends use of a cystatin C-based estimated glomerular filtration rate (eGFR) to confirm creatinine-based eGFR between 45 and 59 mL · min^-1 · (1.73 m²)^-1. Prior studies have demonstrated that comorbidities such as solid-organ transplant strongly influence the relationship between measured GFR, creatinine, and cystatin C. Our objective was to evaluate the performance of cystatin C-based eGFR equations compared with creatinine-based eGFR and measured GFR across different clinical presentations. METHODS: We compared the performance of the CKD-EPI 2009 creatinine-based estimated GFR equation (eGFR_Cr) and the newer CKD-EPI 2012 cystatin C-based equations (eGFR_Cys and eGFR_Cr-Cys) with measured GFR (iothalamate renal clearance) across defined patient populations. Patients (n = 1652) were categorized as transplant recipients (n = 568 kidney; n = 319 other organ), known chronic kidney disease (CKD) patients (n = 618), or potential kidney donors (n = 147). RESULTS: eGFR_Cr-Cys showed the most consistent performance across different clinical populations. Among potential kidney donors without CKD [stage 2 or higher; eGFR >60 mL · min^-1 · (1.73 m²)^-1], eGFR_Cys and eGFR_Cr-Cys demonstrated significantly less bias than eGFR_Cr; however, all 3 equations substantially underestimated GFR when eGFR was <60 mL · min^-1 · (1.73 m²)^-1. Among transplant recipients with CKD stage 3B or greater [eGFR <45 mL · min^-1 · (1.73 m²)^-1], eGFR_Cys was significantly more biased than eGFR_Cr. No clear differences in eGFR bias between equations were observed among known CKD patients regardless of eGFR range or in any patient group with a GFR between 45 and 59 mL · min^-1 · (1.73 m²)^-1. CONCLUSIONS: The performance of eGFR equations depends on patient characteristics that are readily apparent on presentation. Among the 3 CKD-EPI equations, eGFR_Cr-Cys performed most consistently across the studied patient populations.