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

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.研究背景与研究目的：在肾小球滤过率（glomerular filtration rate, GFR）的评估中，种族是一项重要的决定因素。然而，目前所有已有的估算公式均仅基于白种人和非裔美国人人群构建，其在非洲人群中估算GFR的准确性可能不足。因此，本研究旨在评估不同估算肾小球滤过率（estimated GFR, eGFR）公式对实测肾小球滤过率（measured GFR, mGFR）的预测性能。 研究方法：本研究为横断面研究，于2015年6月至2016年4月间，在刚果民主共和国金沙萨的普通人群中随机选取了93名健康成年人。我们以碘海醇血浆清除率测定的mGFR作为金标准，对比了以下多种eGFR公式的计算结果：带种族校正因子与不带种族校正因子的肾脏病饮食改良研究（Modified Diet in Renal Disease, MDRD）公式、带与不带种族校正因子的基于血清肌酐（serum creatinine, SCr）的慢性肾脏病流行病学合作研究（Chronic Kidney Disease Epidemiology, CKD-EPI）公式、基于半胱氨酸蛋白酶抑制剂C的CKD-EPI公式（CKD-EPI SCys），以及带与不带种族校正因子的联合公式（CKD-EPI SCrCys）。通过计算偏倚、精密度以及与mGFR差值在30%以内的准确度（P30），评估各公式的预测性能。 研究结果：本研究纳入的93名受试者中，女性48名，男性45名，平均年龄为45.0±15.7岁，平均体表面积为1.68±0.16m²。受试者的平均mGFR为92.0±17.2 mL/min/1.73m²，范围为57~141 mL/min/1.73m²。不同公式计算得到的平均eGFR如下：带种族校正因子的MDRD公式为105.5±30.1 mL/min/1.73m²，不带种族校正因子的MDRD公式为87.2±24.8 mL/min/1.73m²；带种族校正因子的基于SCr的CKD-EPI公式为108.8±24.1 mL/min/1.73m²，不带种族校正因子的该公式为94.3±20.9 mL/min/1.73m²；CKD-EPI SCys公式的平均eGFR为93.5±18.6 mL/min/1.73m²；带种族校正因子的联合公式CKD-EPI SCrCys为101±19.6 mL/min/1.73m²，不带种族校正因子的该联合公式为93.5±18.0 mL/min/1.73m²。除不带种族校正因子的MDRD公式（低估值为-3.8±23.0 mL/min/1.73m²）外，其余所有公式均轻度高估了mGFR。带种族校正因子的CKD-EPI SCr公式与MDRD公式均显著高估了mGFR，偏倚分别为17.9±19.2 mL/min/1.73m²与14.5±27.1 mL/min/1.73m²。相较于带种族校正因子的对应公式，不带种族校正因子的MDRD与CKD-EPI SCr公式的P30值呈现更优趋势：MDRD公式分别为86.0% vs 79.6%（p=0.21），CKD-EPI SCr公式分别为81.7% vs 73.1%（p=0.057）。CKD-EPI SCys与CKD-EPI SCrCys公式的表现优于基于肌酐的公式。 研究结论：在刚果健康人群中，不带种族校正因子的MDRD与CKD-EPI公式的预测性能优于带种族校正因子的对应公式。基于半胱氨酸蛋白酶抑制剂C（单独使用或与SCr联合使用）的公式，其表现优于基于肌酐的公式。