Significance of the difference in the estimates of glomerular filtration rate obtained using different models

Chronic kidney disease (CKD) prevalence is rising in Nigeria. Most cases are diagnosed as end stage disease despite availability of formulae to estimate glomerular filtration rate (GFR). Existing formulae, none of which is modelled on Nigerian variables, give different estimates. This study tests the significance of the difference in the estimates obtained using Modified Diet in Renal Disease (MDRD) Study and Chronic Kidney Disease-Epidemiology (CKD-Epi) formulae.

This is a cross-sectional study. Data on age, gender, and serum creatinine were used to estimate GFR. Paired sample t test was used to check for difference in means, Pearson correlation test for correlation and Bland and Altman plot for systematic bias. Simple linear regression was used to check for presence and significance of proportional bias.

Of the 166 patients studied, 62 were males and 104 were females. Mean age was 49.06 years ± 15.26. Youngest was 18 years and the oldest 81 years. Mean eGFR of 69.4 and 72.77 ml/min/1.73m² for MDRD and CKD-Epi models respectively differed significantly, P < 0.001. Bland and Altman plot showed lack of agreement of eGFR estimates from the two models with significant bias of -3.37ml/min/1.73m² despite good correlation, r = 0.984. There was significant proportional bias, P < 0.001.

MDRD significantly underestimated GFR compared to CKD-Epi in a Nigerian population. This bias was proportional and increased as mean eGFR increased. MDRD and CKD-Epi models do not agree in their measurements of eGFR and should not be used interchangeably. There is urgent need for further studies to develop GFR estimating model on Nigerian variables.