Division of Nephrology, Department of Internal Medicine, University Medical Center Groningen, Groningen, The Netherlands.
Nephrol Dial Transplant. 2011 Oct;26(10):3181-8. doi: 10.1093/ndt/gfq850. Epub 2011 Mar 3.
Accurate glomerular filtration rate (GFR) measurement in normal to high range is important for epidemiological studies and workup for kidney donation. Creatinine-based equations perform poorly in this GFR range. Creatinine clearance (CrCl) provides a substitute, provided urine is collected accurately and tubular creatinine handling can be accounted for. The latter is poorly characterized in the normal GFR range.
Therefore, we studied performance of CrCl, fractional creatinine excretion (FE(creat)) and its determinants in 226 potential kidney donors (47% males, mean 53 ± 10 years). GFR was assessed as (125)I-iothalamate clearance, simultaneously with 2-h CrCl and 24-h CrCl.
Mean GFR was 101 ± 18, 2-h CrCl 110 ± 20 and 24-h CrCl 106 ± 29 mL/min/1.73 m(2). Mean bias of 24 h CrCl was 7.4 [inter-quartile range -6.7 to 20.0] mL/min/1.73 m(2), precision (R(2)) 0.39 and 30% accuracy 82%. Mean FE(creat) was 110 ± 11%. FE(creat) correlated with body mass index (BMI) (r = 0.34, P < 0.001). Consequently, bias of 24-h CrCl increased from 2.7 (inter-quartile range -6.5 to 16.7) to 8.6 (inter-quartile range -5.8 to 20.5) and 12.6 (inter-quartile range 7.0 to 25.4) mL/min in subjects with BMI <25, 25-30 and >30 kg/m(2), respectively (P < 0.05). On multivariate analysis, BMI and gender were predictors of FE(creat).
CrCl systematically overestimates GFR in healthy subjects. The overestimation significantly correlates with BMI, with higher FE(creat) in subjects with higher BMI. The impact of BMI on tubular creatinine secretion can be accounted for, when using CrCl for GFR assessment in the normal to high range, by the following formula: GFR = 24-h CrCl - (22.75 + 0.76 × BMI - 0.29 × mean arterial pressure (-6.11 if female).
在正常到高范围内准确测量肾小球滤过率（GFR）对于流行病学研究和肾脏捐献的评估非常重要。基于肌酐的方程在该 GFR 范围内表现不佳。肌酐清除率（CrCl）可以替代，但前提是准确收集尿液并能考虑肾小管肌酐的处理。在正常 GFR 范围内，后者的特征描述较差。
因此，我们研究了 226 名潜在肾脏供体（47%为男性，平均年龄 53±10 岁）的 CrCl、分数肌酐排泄率（FE(creat))及其决定因素的性能。GFR 评估为（125）I-碘酞酸盐清除率，同时进行 2 小时 CrCl 和 24 小时 CrCl。
平均 GFR 为 101±18、2 小时 CrCl 为 110±20 和 24 小时 CrCl 为 106±29 mL/min/1.73 m(2)。24 小时 CrCl 的平均偏差为 7.4[四分位距（IQR）为-6.7 至 20.0]mL/min/1.73 m(2)，精度（R(2))为 0.39，30%的准确性为 82%。平均 FE(creat)为 110±11%。FE(creat)与体重指数（BMI）相关（r=0.34，P<0.001）。因此，24 小时 CrCl 的偏差从 BMI<25、25-30 和>30 kg/m(2)的受试者中分别从 2.7（IQR-6.5 至 16.7）增加到 8.6（IQR-5.8 至 20.5）和 12.6（IQR-7.0 至 25.4）mL/min（P<0.05）。多元分析显示，BMI 和性别是 FE(creat)的预测因子。
CrCl 在健康受试者中系统地高估了 GFR。高估与 BMI 显著相关，BMI 较高的受试者的 FE(creat)较高。当在正常到高范围内使用 CrCl 评估 GFR 时，通过以下公式可以考虑 BMI 对肾小管肌酐分泌的影响：GFR=24 小时 CrCl-（22.75+0.76×BMI-0.29×平均动脉压（女性为-6.11））。
