Supplementary Material for: Renal Function Assessment Gap in Clinical Practice: An Awkward Truth

<b><i>Introduction:</i></b> An accurate assessment of renal function is needed in the majority of clinical settings. Unfortunately, the most used estimated glomerular filtration rate (eGFR) formulas are affected by significant errors in comparison to gold standards methods of measured GFR (mGFR). <b><i>Objective:</i></b> The objective of the study is to determine the extent of the error of eGFR formulas compared to the mGFR in different specific clinical settings. <b><i>Methods:</i></b> A total retrospectively consecutive cohort of 1,320 patients (pts) enrolled in 2 different European Hospitals (Center 1: 470 pts; Center 2: 850 pts) was collected in order to compare the most common eGFR formulas used by physicians with the most widespread mGFR methods in daily clinical practice (Iohexol Plasma Clearance -Center 1 [mGFR-iox] and Renal Scintigraphy -Center 2 [mGFR-scnt]). The study cohort was composed by urological, oncological, and nephrological pts. The agreement between eGFR and mGFR was evaluated using bias (as median of difference), precision (as interquartile range of difference) accuracy (as P₃₀), and total deviation index. <b><i>Results:</i></b> The most accurate eGFR formula in the comparison with gold standard method (Iohexol plasma clearance) in Center 1 was represented by s-creatinine and cystatin C combined Chronic Kidney Disease-Epidemiology Collaboration-cr-cy, even though the P₃₀ is reduced (84%) under the threshold of 60 mL/min/1.73 m². Similar results were found in Center 2, with a wider discrepancy between mGFR-scnt and eGFR formulas due to the minor accuracy of the nuclear tool in respect to the mGFR-iox. <b><i>Conclusions:</i></b> The loss of accuracy observed for the formulas at lower values of GFR suggests the mandatory use of gold standards methods as Iohexol Plasma Clearance to assess the correct status of renal function for critical cases. The center 2 showed lower levels of agreement between mGFR and eGFR suggesting that the errors are partially accounted for the Renal Scintigraphy technique too. In particular, we suggest the use of mGFR-iox in oncological urological and nephrological pts with an eGFR lower than 60 mL/min/1.73 m².

**引言：** 绝大多数临床场景均需对肾功能进行精准评估。遗憾的是，相较于实测肾小球滤过率（measured GFR, mGFR）的金标准检测方法，当前临床最常用的估算肾小球滤过率（estimated glomerular filtration rate, eGFR）公式均存在显著误差。
**研究目的：** 本研究旨在明确不同特定临床场景下，各类eGFR公式相较于mGFR的误差程度。
**研究方法：** 本研究收集了来自2家欧洲医院的1320例患者的回顾性连续队列数据（中心1：470例；中心2：850例），用于对比临床医师常用的eGFR公式与日常临床实践中最普及的mGFR检测方法：中心1采用碘海醇血浆清除率法（Iohexol Plasma Clearance, mGFR-iox），中心2采用肾显像法（Renal Scintigraphy, mGFR-scnt）。该研究队列涵盖泌尿外科、肿瘤科及肾内科患者。本研究通过偏差（以差值的中位数表示）、精密度（以差值的四分位间距表示）、准确度（以P₃₀表示）及总偏差指数，评估eGFR与mGFR之间的一致性。
**研究结果：** 在中心1，与金标准检测方法（碘海醇血浆清除率法）对比时，准确度最高的eGFR公式为血清肌酐联合胱抑素C的慢性肾脏病-流行病学协作组（Chronic Kidney Disease-Epidemiology Collaboration, CKD-EPI-cr-cy）公式，即便当肾小球滤过率低于60 mL/min/1.73m²时，其P₃₀仅为84%。中心2得到了相似的结果，但mGFR-scnt与eGFR公式间的差异更为显著，这是因为相较于mGFR-iox，肾显像这一核医学检测手段的准确度稍低。
**结论：** 在肾小球滤过率较低的患者中，现有eGFR公式的准确度出现明显下降，这提示对于危重病例，必须采用如碘海醇血浆清除率法这类金标准检测方法以准确评估肾功能状态。中心2中mGFR与eGFR的一致性更低，这表明检测误差也部分来源于肾显像技术本身。尤其建议对于eGFR低于60 mL/min/1.73m²的泌尿外科、肿瘤科及肾内科患者，采用mGFR-iox进行检测。