Gautschi K, Keller B, Keller H, Pei P, Vonderschmitt D J
Institut für Klinische Chemie, Universitätsspital, Zürich, Schweiz.
Eur J Clin Chem Clin Biochem. 1993 Jul;31(7):433-40. doi: 10.1515/cclm.1993.31.7.433.
The relationship between the concentration of the analyte and the imprecision of an analytical method can be displayed by the precision profile in which the coefficient of variation (relative standard deviation) is plotted against the concentration of the analyte. The function of the curve of the profile and its confidence limits can easily be assessed by a computer program developed by W.A. Sadler & M.H. Smith (Clin. Chem. 36 (1990), 1346-1350). For the assessment of limits of detection and of quantification the following procedure is proposed: The lower (and upper) limit of the measuring interval is defined by the point at which an acceptable CV-line intersects the confidence limit. If, in the variance function one sets the concentration to zero, the normal distribution of the random errors of the blank will result. The mean of the next adjacent normal distribution, following the variance formula and overlapping the "zero-distribution" by a defined amount, represents the limit of detection. Within the described measuring interval, or within a fraction of it, one might construct overlapping normal distributions in an analogous manner. Their number represents the "power of definition" (PD) (instead of the "analytical sensitivity"), which also depends on the concentration of the determinand according to the variance function. We tested these hypotheses by a comparison of two methods for the determination of cyclosporin A (ciclosporin, INN). Our results demonstrate that the data of the lower limits of the measuring interval and of the limit of detection agree well with data from the literature obtained in extensive interlaboratory surveys.
分析物浓度与分析方法的不精密度之间的关系可以通过精密度曲线来展示，其中变异系数（相对标准偏差）相对于分析物浓度进行绘制。通过W.A. Sadler和M.H. Smith开发的计算机程序（《临床化学》36 (1990), 1346 - 1350），可以轻松评估该曲线及其置信限的函数。为了评估检测限和定量限，建议采用以下程序：测量区间的下限（和上限）由可接受的CV线与置信限相交的点定义。如果在方差函数中将浓度设为零，将得到空白随机误差的正态分布。按照方差公式，下一个相邻正态分布的均值与“零分布”有一定程度的重叠，该均值代表检测限。在所描述的测量区间内，或在其一部分内，可以以类似的方式构建重叠的正态分布。它们的数量代表“定义能力”（PD）（而非“分析灵敏度”），其也根据方差函数取决于被测定物的浓度。我们通过比较两种测定环孢素A（环孢菌素，国际非专利药品名称）的方法对这些假设进行了检验。我们的结果表明，测量区间下限和检测限的数据与在广泛的实验室间调查中从文献获得的数据吻合良好。
