Laboratory Medicine Department, La Paz-Cantoblanco-Carlos III University Hospital, Madrid, Spain.
Laboratory Medicine Department, Hospital Universitari Son Espases, Palma, Spain.
Clin Chem Lab Med. 2019 Nov 26;57(12):1829-1836. doi: 10.1515/cclm-2019-0586.
Stability of a measurand in a specimen is a function of the property variation over time in specific storage conditions, which can be expressed as a stability equation, and is usually simplified to stability limits (SLs). Stability studies show differences or even inconsistent results due to the lack of standardized experimental designs and heterogeneity of the chosen specifications. Although guidelines for the validation of sample collection tubes have been published recently, the measurand stability evaluation is not addressed. This document provides an easy guideline for the development of a stability test protocol based on a two-step process. A preliminary test is proposed to evaluate the stability under laboratory habitual conditions. The loss of stability is assessed by comparing measurement values of two samples obtained from the same patient and analyzed at different time points. One of them is analyzed under optimal conditions (basal sample). The other is stored under specific stability conditions for a time set by the laboratory (test sample). Differences are expressed using percentage deviation (PD%) to facilitate comparison with specifications. When the preliminary test demonstrates instability, a comprehensive test is proposed in order to define the stability equation and to specify SLs. Several samples are collected from a set of patients. The basal sample is analyzed under optimal conditions, whereas analysis of test samples is delayed at time intervals. For each patient PD% is calculated as the difference between measurements for every test sample and its basal one and represented in a coordinate graph versus time.
标本中测量值的稳定性是特定储存条件下随时间变化的特性的函数，可用稳定性方程表示，通常简化为稳定性限度（SLs）。由于缺乏标准化的实验设计和所选规格的异质性，稳定性研究显示出差异，甚至不一致的结果。尽管最近已经发布了采集管样本验证的指南，但并未涉及测量值稳定性评估。本文件提供了一种基于两步法制定稳定性测试方案的简便指南。建议进行初步测试以评估实验室常规条件下的稳定性。通过比较同一患者的两个样本的测量值来评估稳定性的丧失，这两个样本在不同时间点进行分析。其中一个在最佳条件下（基础样本）进行分析。另一个在实验室设定的特定稳定性条件下（测试样本）进行储存。使用百分比偏差（PD%）表示差异，以方便与规格进行比较。当初步测试显示不稳定时，建议进行全面测试以确定稳定性方程并指定 SLs。从一组患者中采集多个样本。基础样本在最佳条件下进行分析，而测试样本的分析则在时间间隔内延迟。对于每个患者，PD% 计算为每个测试样本与其基础样本之间的测量值之差，并以坐标图表示随时间的变化。
