Schoeller D A, Taylor P B
Hum Nutr Clin Nutr. 1987 May;41(3):215-23.
The intrasubject precision of the doubly labelled water method was investigated as a function of increasing length of the metabolic period and decreasing initial isotope enrichment. This analysis was performed in seven subjects following a single dose of isotope and three subjects who received multiple doses of isotope. The intrasubject precision was 5-6 per cent for periods of up to 14 d. This is only slightly larger than that predicted from our previously published model in which we assumed that analytical error was limiting precision. Intrasubject precision worsened with increasing length of the metabolic period and with decreasing initial isotope enrichment, but the loss of precision was two to ten times greater than that predicted by the model. The use of the intercept method to determine the isotope dilution spaces did not improve precision. We speculate that one cause of the failure of the model is that it does not consider unmeasured changes in natural isotopic abundances associated with dietary intake. Results demonstrate the importance of choosing a dose that provides an initial isotope enrichment that is 500-600 times the analytical error, and a metabolic period that is between one and three biological half-lives of the isotopic tracers.
作为代谢期延长和初始同位素富集度降低的函数，对双标记水法的个体内精密度进行了研究。在7名单次接受同位素剂量的受试者和3名多次接受同位素剂量的受试者中进行了此项分析。在长达14天的时间段内，个体内精密度为5% - 6%。这仅略高于我们之前发表的模型所预测的值，在该模型中我们假设分析误差限制了精密度。个体内精密度随着代谢期延长和初始同位素富集度降低而变差，但精密度的损失比模型预测的大2至10倍。使用截距法确定同位素稀释空间并未提高精密度。我们推测该模型失败的一个原因是它没有考虑与饮食摄入相关的天然同位素丰度的未测量变化。结果表明，选择一个能提供初始同位素富集度为分析误差500 - 600倍的剂量以及处于同位素示踪剂1至3个生物半衰期之间的代谢期的重要性。
