Laboratoire National de Métrologie et d'Essais, Department of Biomedical and Organic Chemistry, 1 Rue Gaston Boissier, Paris, France.
Clin Biochem. 2013 Mar;46(4-5):359-64. doi: 10.1016/j.clinbiochem.2012.11.026. Epub 2012 Dec 5.
Our objective was to develop a reference method to measure total cholesterol in human serum, in order to assign values and assess the accuracy of field methods in French clinical laboratories.
A reference method based on gas chromatography coupled with mass spectrometry and isotope dilution (GC-IDMS) was developed and validated. It was then used to assign reference values to five frozen serum samples from voluntary proficiency testing schemes gathering 170 French clinical laboratories. Three peer groups were defined and bias against the reference method target value was calculated.
Accuracy of the reference method was assessed against NIST SRM 1951b. Bias of the reference method was less than 0.5% and imprecision was less than 1.0%. Our study indicated that field methods tended to overestimate total cholesterol concentration, mean bias being +5.02% ± 1.02%. The most popular methods (phenolic chromogen with spectrophotometric detection, 80% of participants) exhibited the highest bias (peer group mean bias: +5.51 ± 1.24%). Neither these methods nor those using a non-phenolic chromogen with reflectometric detection (10% of participants, peer group mean bias: +4.20 ± 1.44%) met NCEP recommendations according to which bias should be less than 3%. Only the methods using a non phenolic chromogen with a spectrophotometric detection met these recommendations (10% of participants, peer group mean bias: +1.39 ± 2.75%).
As all three peer groups provided positively biased results, the consensus mean usually used to assess the trueness of routine methods is biased as well, which results in an erroneous estimation of method bias. Therefore, this study highlights the value added by reference method target values to assess trueness of field methods and monitor performance of clinical laboratories.
本研究旨在建立一种测量人血清总胆固醇的参考方法，以便为法国临床实验室的现场方法赋值和评估其准确性。
建立了一种基于气相色谱-质谱联用和同位素稀释（GC-IDMS）的参考方法，并对其进行了验证。然后，使用该方法对来自自愿参加能力验证计划的五个冷冻血清样本赋值，该计划共汇集了 170 个法国临床实验室。定义了三个同行组，并计算了与参考方法目标值的偏倚。
参考方法的准确性通过 NIST SRM 1951b 进行评估。参考方法的偏差小于 0.5%，不精密度小于 1.0%。本研究表明，现场方法往往高估总胆固醇浓度，平均偏倚为+5.02%±1.02%。最受欢迎的方法（80%的参与者使用酚类显色剂进行分光光度检测）表现出最高的偏倚（同行组平均偏倚：+5.51±1.24%）。根据 NCEP 的建议，这些方法和使用非酚类显色剂进行反射光度检测的方法（10%的参与者，同行组平均偏倚：+4.20±1.44%）都不符合要求，即偏差应小于 3%。只有使用非酚类显色剂进行分光光度检测的方法符合这些建议（10%的参与者，同行组平均偏倚：+1.39±2.75%）。
由于所有三个同行组都提供了正偏倚的结果，因此通常用于评估常规方法准确性的共识平均值也存在偏倚，这导致对方法偏倚的错误估计。因此，本研究强调了参考方法目标值在评估现场方法准确性和监测临床实验室性能方面的价值。
