Performance of glomerular filtration rate estimation equations in Congolese healthy adults: The inopportunity of the ethnic correction

Abstract

Context and objectiveIn the estimation of glomerular filtration rate (GFR), ethnicity is an important determinant. However, all existing equations have been built solely from Caucasian and Afro-American populations and they are potentially inaccurate for estimating GFR in African populations. We therefore evaluated the performance of different estimated GFR (eGFR) equations in predicting measured GFR (mGFR).MethodsIn a cross-sectional study, 93 healthy adults were randomly selected in the general population of Kinshasa, Democratic Republic of the Congo, between June 2015 and April 2016. We compared mGFR by plasma clearance of iohexol with eGFR obtained with the Modified Diet in Renal Disease (MDRD) equation with and without ethnic factor, the Chronic Kidney Disease Epidemiology (CKD-EPI) serum creatinine (SCr)-based equation, with and without ethnic factor, the cystatin C-based CKD-EPI equation (CKD-EPI SCys) and with the combined equation (CKD-EPI SCrCys) with and without ethnic factor. The performance of the equations was studied by calculating bias, precision and accuracy within 30% (P30) of mGFR.ResultsThere were 48 women and 45 men. Their mean age was 45.0±15.7 years and the average body surface area was 1.68±0.16m2. Mean mGFR was 92.0±17.2 mL/min/1.73m2 (range of 57 to 141 mL/min/1.73m2). Mean eGFRs with the different equations were 105.5±30.1 and 87.2±24.8 mL/min/1.73m2 for MDRD with and without ethnic factor, respectively; 108.8±24.1 and 94.3x20.9 mL/min/1.73m2 for CKD-EPI SCr with and without ethnic factor, respectively, 93.5±18.6 mL/min/1.73m2 for CKD-EPI SCys; 93.5±18.0 and 101±19.6 mL/min/ 1.73m2 for CKD-EPI SCrCys with and without ethnic factor, respectively. All equations slightly overestimated mGFR except MDRD without ethnic factor which underestimated by -3.8±23.0 mL/min /1.73m2. Both CKD-EPI SCr and MDRD with ethnic factors highly overestimated mGFR with a bias of 17.9±19.2 and 14.5±27.1 mL/min/1.73m2, respectively. There was a trend for better P30 for MDRD and CKD-EPI SCr without than with the ethnic factor [86.0% versus 79.6% for MDRD (p = 0.21) and 81.7% versus 73.1% for the CKD-EPI SCr equations (p = 0.057)]. CKD-EPI SCrCys and CKD-EPI SCys were more effective than creatinine-based equations.ConclusionIn the Congolese healthy population, MDRD and CKD-EPI equations without ethnic factors had better performance than the same equations with ethnic factor. The equations using Cys C (alone or combined with SCr) performed better than the creatinine-based equations.

Performance of creatinine- or cystatin C–based equations to estimate glomerular filtration rate in sub-Saharan African populations

“…21 Previous data from Africa (and African European) also suggested that such an ethnic factor was not valuable. [18][19][20][21][22]29,30 Regarding ethnicity, we showed that FAS SCr af had the same global performance as FAS SCr observed in Whites, both in patients with low GFR values and in subjects with high GFR values. This is easily explained, as Q af was not different from the Q values observed in Whites.…”

“…In DRC, healthy persons were randomly selected from the general population as described elsewhere. 19 Healthy subjects were all those who did not have hypertension, diabetes mellitus, obesity, urinary abnormalities, and impaired renal function (GFR <60 or >130 ml/ min per 1.73 m 2 ). Patients with CKD were recruited from the general population and from the medical services (Renal Unit of Kinshasa University Hospital).…”

“…Also, relatively few studies have considered the performance of the CKD-EPI and MDRD equations in African people, and most were focused on healthy adult black Africans and/or in one country. [18][19][20] In the present analysis, we evaluated the performance of different equations (Table 1) for GFR estimation in a large cohort of sub-Saharan African people from 2 countries, including patients with CKD. Our goal was to study 3 topics of clinical interest for nephrologists in Africa regarding estimating GFR.…”

“…The MDRD and CKD-EPI equations were thus considered and compared with and without the African American ethnic factors (ef) (MDRD ef or MDRD and CKD-EPI ef or CKD-EPI). 18,19,21,22 In the same view, specific Q values for African people were proposed for the creatinine-based FAS equation. The creatinine-based FAS equation was considered with these Q values (FAS af) or with the values for Whites (FAS).…”

Estimating Residual Kidney Function: Present and Future Challenge

“…New equations can be useful not only for CKD patients but also for other special cases which are not covered by the present creatinine-based GFR-estimating formulas, such as nonwhite, non-African American, despite ethnic correction [28,29]. During the past decade, alternative markers for GFR, such as cystatin C (CysC), B2 microglobulin (B2M), betatrace protein (BTP), and others have emerged [27,[30][31][32][33][34].…”