Division of Internal Medicine-Nephrology, Department of Medicine, Faculty of Medicine, Chulalongkorn University and King Chulalongkorn Memorial Hospital, Thai Red Cross Society, Bangkok, Thailand.
Special Task force for Activating Research in Renal Nutrition (Renal Nutrition Research Group), Office of Research Affairs, Chulalongkorn University, Bangkok, Thailand.
PLoS One. 2020 Nov 18;15(11):e0242447. doi: 10.1371/journal.pone.0242447. eCollection 2020.
Obesity is a major public health with increasing numbers of obese individuals are at risk for kidney disease. However, the validity of serum creatinine-based glomerular filtration rate (GFR) estimating equations in obese population is yet to be determined.
We evaluated the performance of the reexpressed Modification of Diet in Renal Disease (MDRD), reexpressed MDRD with Thai racial factor, Thai estimated GFR (eGFR) as well as Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations among obese patients, defined as body mass index (BMI) ≥25 kg/m2 with the reference measured GFR (mGFR) determined by 99mTc-diethylene triamine penta-acetic acid (99mTc-DTPA) plasma clearance method. Serum creatinine levels were measured using standardized enzymatic method simultaneously with GFR measurement. The statistical methods in assessing agreement for continuous data including total deviation index (TDI), concordance correlation coefficient (CCC), and coverage probability (CP) for each estimating equation were compared with the reference mGFR. Accuracy within 10% representing the percentage of estimations falling within the range of ±10% of mGFR values for all equations were also tested.
A total of 240 Thai obese patients were finally recruited with mean BMI of 31.5 ± 5.8 kg/m2. In the total population, all eGFR equations underestimated the reference mGFR. The average TDI values were 55% indicating that 90% of the estimates falling within the range of -55 to +55% of the reference mGFR. The CP values averaged 0.23 and CCC scores ranged from 0.75 to 0.81, reflecting the low to moderate levels of agreement between each eGFR equation and the reference mGFR. The proportions of patients achieving accuracy 10% ranged from 23% for the reexpressed MDRD equation to 33% for the Thai eGFR formula. Among participants with BMI more than 35 kg/m2 (n = 48), the mean error of all equations was extremely wide and significantly higher for all equations compared with the lower BMI category. Also, the strength of agreement evaluated by TDI, CCC, and CP were low in the subset of patients with BMI ≥35 kg/m2.
Estimating equations generally underestimated the reference mGFR in subjects with obesity. The overall performance of GFR estimating equations demonstrated poor concordance with the reference mGFR among individuals with high BMI levels. In certain clinical settings such as decision for dialysis initiation, the direct measurements of GFR are required to establish real renal function among obese population.
肥胖是一个主要的公共卫生问题，越来越多的肥胖个体面临肾脏疾病的风险。然而，基于血清肌酐的肾小球滤过率（GFR）估计方程在肥胖人群中的有效性尚待确定。
我们评估了重新表达的肾脏病饮食改良（MDRD）公式、重新表达的包含泰国人群种族因素的 MDRD 公式、泰国估计 GFR（eGFR）公式以及慢性肾脏病流行病学合作（CKD-EPI）公式在肥胖患者中的表现，肥胖患者的定义为 BMI≥25kg/m2，参考测量的 GFR（mGFR）由 99mTc-二乙三胺五乙酸（99mTc-DTPA）血浆清除率方法确定。同时测量 GFR 时使用标准化酶法测量血清肌酐水平。用于评估连续数据一致性的统计方法包括总偏差指数（TDI）、一致性相关系数（CCC）和每个估计方程的覆盖概率（CP），并与参考 mGFR 进行比较。所有方程的准确性均在 10%以内，代表估计值落在 mGFR 值的±10%范围内的百分比。
共招募了 240 名泰国肥胖患者，平均 BMI 为 31.5±5.8kg/m2。在总人群中，所有 eGFR 方程均低估了参考 mGFR。平均 TDI 值为 55%，这表明 90%的估计值落在参考 mGFR 的-55%至+55%范围内。CP 值平均为 0.23，CCC 评分范围为 0.75 至 0.81，反映了每个 eGFR 方程与参考 mGFR 之间的低到中度一致性。达到准确性 10%的患者比例范围为重新表达的 MDRD 方程的 23%至泰国 eGFR 公式的 33%。在 BMI 超过 35kg/m2 的参与者中（n=48），所有方程的平均误差非常大，与较低 BMI 类别相比，所有方程的误差都明显更高。此外，在 BMI≥35kg/m2 的患者亚组中，通过 TDI、CCC 和 CP 评估的一致性强度较低。
估计方程通常低估了肥胖个体的参考 mGFR。在 BMI 较高的个体中，GFR 估计方程的整体表现与参考 mGFR 显示出较差的一致性。在某些临床情况下，例如开始透析的决策，需要直接测量 GFR 以确定肥胖人群的真实肾功能。
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