New analysis of the comparative diagnostic performances of five different eGFR equations: The revised 2021 CKD-EPI eGFR, and the four older equations

Purpose: In 2021, the CKD-EPI-creatinine and CKD-EPI-creatinine-cystatin-C combined equations were revised again by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and the National Institute of Diabetes & Digestive and Kidney Diseases (NIDDK) and it was reported that its accuracy was increased. The main object of this study is to compare the diagnostic accuracy and performance of 2009 CKD-EPI eGFRcr, 2012 CKD-EPI eGFRCysC, 2012 CKD-EPI eGFRcr-CysC, MDRD, and revised 2021 CKD-EPI to provide a better estimation. 
Materials and Methods: The study design was prospective. The sample consisted of 111 CKD patients and 35 healthy individuals who applied to the nephrology clinic. All participants were evaluated by a nephrologist. The participants were divided into study groups according to their KDIGO classification. Five variables were used: age, race, gender, serum creatinine, and serum cystatin-C. 
Results: 2012 CKD-EPI eGFR cystatin-C out performed existing equations in terms of accuracy, specificity, and sensitivity (AUC:0.988). Furthermore, when both creatinine and cystatin-C are included in an equation, it consistently improves diagnostic values over formulas containing only creatinine (2009CKD-EPI eGFRcr AUC:0.953, 2012CKD-EPI eGFRcr-CysC AUC: 0.985, 2021CKD-EPI eGFRcr AUC:0.954, MDRD AUC: 0.953, 2021CKD-EPI eGFRcr-CysC AUC: 0.985). 
Conclusion: The new formula has not been confirmed to be superior to other equations in its ability to estimate eGFR values, particularly at higher levels of chronic kidney disease. When compared with existing equations, 2012 CKD-EPI eGFRCysC had higher specificity and sensitivity. Combined formulas containing both blood tests had higher diagnostic values than equations containing only creatinine. Our results can help inform which equations to use for better estimation in renal function screening.