Fleming John S
Department of Medical Physics and Bioengineering, Southampton University Hospitals NHS Trust, UK.
Nucl Med Commun. 2007 Apr;28(4):315-20. doi: 10.1097/MNM.0b013e328014a14a.
Glomerular filtration rate (GFR) is commonly assessed by plasma sampling using the slope-intercept technique. This method assumes a single exponential approximation to the plasma curve. To obtain an accurate estimate of GFR it is necessary to correct the slope-intercept value for the approximation. This is commonly done using the Brochner-Mortensen equation. This has been validated for normal and abnormally low GFRs, but there has been some suggestion that it may underestimate supra-normal GFR. This paper investigates this suggestion and aims to produce a new equation based on compartmental analysis, which should extrapolate the correction to higher values of GFR.
Compartmental analysis was used to produce the complete expression of the relationship between true GFR and slope-intercept GFR. A simplified analytical equation was then derived. The performance of the new equation was compared to the Brochner-Mortensen and Chantler equations using the true GFR as reference.
The new analytical equation had minimal systematic error compared to true GFR up to 250 ml x min(-1) per 1.73 m(2). The Brochner-Mortensen equation was shown to underestimate high values of GFR. The error increased with GFR with a 10% underestimation at 180 ml x min(-1) per 1.73 m(2). The Chantler equation gave a systematic overestimate of GFR. The error increased with GFR with a 30% overestimate at 180 ml x min(-1) per 1.73 m(2).
The new equation described in this paper gave considerably improved correction for the single exponential approximation at high GFR compared to previously described equations.
肾小球滤过率（GFR）通常采用斜率截距法通过血浆采样进行评估。该方法假定血浆曲线呈单指数近似。为获得GFR的准确估计值，有必要对该近似值的斜率截距值进行校正。这通常使用布罗克纳 - 莫滕森方程来完成。该方程已在正常和异常低的GFR情况下得到验证，但有一些迹象表明它可能会低估高于正常的GFR。本文对这一迹象进行研究，并旨在基于房室分析得出一个新方程，该方程应能将校正外推至更高的GFR值。
采用房室分析得出真实GFR与斜率截距GFR之间关系的完整表达式。然后推导出一个简化的分析方程。以真实GFR为参考，将新方程的性能与布罗克纳 - 莫滕森方程和钱特勒方程进行比较。
与真实GFR相比，新的分析方程在高达250 ml·min⁻¹/1.73 m²时系统误差最小。结果表明布罗克纳 - 莫滕森方程会低估高值的GFR。误差随GFR增加，在180 ml·min⁻¹/1.73 m²时低估10%。钱特勒方程会系统性高估GFR。误差随GFR增加，在180 ml·min⁻¹/1.73 m²时高估30%。
与先前描述的方程相比，本文所述的新方程在高GFR时对单指数近似的校正有显著改进。
