Comparison of CKD-EPI versus MDRD and Cockcroft-Gault equations to estimate glomerular filtration rate among stable homozygous sickle cell patients in Southwest Nigeria

Abstract

Background: Homozygous sickle cell patients are prone to renal damage which can be on-going in and out of crises, therefore, there is a need to monitor renal status using glomerular filtration rate. Equations to estimate GFR are readily available. Cockcroft-Gault equation is widely used, while the MDRD formula is the currently accepted equation. The CKD-EPI equation is recently being recommended but has not been validated among HbSS patients. Therefore, we aim to compare estimated GFR using CKD-EPI versus MDRD and Cockcroft-Gault equations among HbSS patients.

Material and Methods: This was a cross-sectional study of stable HbSS patients. Information on their age, sex, and weight was collected. Their venous blood samples were also obtained for plasma creatinine determination which was used to calculate estimated GFR using Cockcroft-Gault, MDRD and CKDEPI equations. Student t-test, Pearson correlation, and Bland-Altman difference plots were performed. A p-value of < 0.05 was considered to be significant.

Results: One hundred and twenty patients comprising 60 HbSS patients and 60 HbAA controls participated in the study. The HbSS patients had mean ± SD age of 26±6.7years, plasma creatinine 77 ± 17umol/L, eGFR: CG 93±31.6ml/min, MDRD 124 ± 34.8ml/min/1.73m², CKD-EPI 122 ± 25.1ml/min/1.73m² (p<0.0001). Hyperfiltration was observed in 20(33.3%) of the HbSS patients. CKD-EPI had stronger positive correlation with MDRD (n = 60, r = 0.93) and less bias (SD = 14.7) than with CG (n = 60, r = 0.76, SD = 20).

Conclusion: CKD-EPI equation is best for individuals with GFR > 60ml/min/1.73m². This study has shown that it correlates well with the currently acceptable MDRD equation, therefore, can be used to monitor the renal status of stable HbSS patients. CG gives poor correlation and bias with CKD-EPI. Further validation studies on CKD-EPI equation are needed in different patient populations.

Keywords: CKD-EPI, Cockcroft-Gault equation, Glomerular filtration rate, MDRD equation, sickle cell anaemia