Performance of creatinine and cystatin C-based equations for estimating high levels of glomerular filtration rate in Congolese adults with sickle cell disease

Introduction: Sickle cell disease (SCD) carries a high risk of chronic kidney disease, necessitating accurate glomerular filtration rate (GFR) monitoring. This study evaluated the performance of creatinine-based (eGFRcrea), cystatin C-based (eGFRcys), and combined (eGFRcrea+cys) equations against directly measured GFR (mGFR). Methods: Clinically stable Congolese adults with SCD were recruited in 13 medical centers from Kinshasa. GFR was measured using iohexol plasma clearance. We compared the bias, precision, and accuracy of Chronic Kidney Disease Epidemiology (CKD-EPI) and European Kidney Function Consortium (EKFC) equations. Results: Among 207 patients included (24 [20;31] years and 58% of women), mean mGFR was 129 ± 38 ml/min/1.73 m2 with 41% of patients hyperfiltrating (mGFR >135 ml/min/1.73 m2). Among eGFRcrea equations, CKD-EPI was superior in hyperfiltrating patients, while EKFC performed better in normofiltrating patients. However, all eGFRcrea equations were suboptimal with only around 80% of estimated GFR (eGFR) results within 30% of mGFR. eGFRcys equations showed severe underestimation and poor accuracy. eGFRcrea+cys equations offered no clear added value. Conclusion: All eGFR equations were suboptimal in this young SCD population, with cystatin C performing particularly poorly. Given the limitations of current biomarkers, measuring GFR by a reference method remains the recommended standard. However, given the cost and logistical challenges of mGFR in low-income settings, relying on creatinine-based EKFC equation for normofiltrating patients and on creatinine based Chronic Kidney Disease Epidemiology Equation (CKD-EPIcrea) for hyperfiltrants appears to be a more feasible and pragmatic approach.