Accuracy and precision of the CKD-EPI and MDRD predictive equations compared with glomerular filtration rate measured by inulin clearance in a Saudi population

BACKGROUND: Predictive equations for estimating glomerular filtration rate (GFR) in different clinical conditions should be validated by comparing with the measurement of GFR using inulin clearance, a highly accurate measure of GFR. OBJECTIVES: Our aim was to validate the Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) and Modification of Diet in Renal Disease (MDRD) equations by comparing it to the GFR measured using inulin clearance in chronic kidney disease (CKD) patients. DESIGN: Cross-sectional study performed in adult Saudi patients with CKD. SETTING: King Saud University Affiliated Hospital, Riyadh, Saudi Arabia in 2014. PATIENTS AND METHODS: We compared GFR measured by inulin clearance with the estimated GFR calculated using CKD-EPI and MDRD predictive formulas. MAIN OUTCOME MEASURE(S): Correlation, bias, precision and accuracy between the estimated GFR and inulin clearance. RESULTS: Comparisons were made in 31 participants (23 CKD and 8 transplanted), including 19 males (mean age 42.2 [15] years and weight 68.7 [18] kg). GFR using inulin was 51.54 (33.8) mL/min/1.73 m(2). In comparison to inulin clearance, the GFR by the predictive equations was: CKD-EPI creatinine 52.6 (34.4) mL/min/1.73 m(2) (P=. 490), CKD-EPI cystatin C 41.39 (30.30) mL/min/1.73 m(2) (P=. 002), CKD creatinine-cystatin C 45.03 (30.9) mL/min/1.73 m(2) (P=. 004) and MDRD GFR 48.35 (31.5) mL/min/1.73 m(2) (P=. 028) (statistical comparisons vs inulin). Bland-Altman plots demonstrated that GFR estimated by the CKD-EPI creatinine was the most accurate compared with inulin clearance, having a mean difference (estimated bias) and limits of agreement of -1.1 (15.6,-17.7). By comparison the mean differences for predictive equations were: CKD-EPI cystatin C 10.2 (43.7,-23.4), CKD creatinine-cystatin C 6.5 (29.3,-16.3) and MDRD 3.2 (18.3,-11.9). Except for CKD-EPI creatinine, all of the equations underestimated GFR in comparison with inulin clearance. CONCLUSIONS: When compared with inulin clearance, the CKD-EPI creatinine equation is the most accurate, precise and least biased equation for estimation of GFR in the Saudi population and in all subgroups by age, stage of CKD and transplantation status. LIMITATIONS: Small sample size and the study did not include patients with comorbid diseases such as diabetes, hepatitis C virus infection, and other co-morbidities as well as old age (>80 years).