A protocol for testing the stability of biochemical analytes. Technical document

Abstract

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.

Influence of study model, baseline catalytic concentrations and analytical system on the stability of serum alanine aminotransferase

“…Percent deviation (PD) from the initial value was used as the basic statistic (initial catalytic concentration − final catalytic concentration)/initial catalytic concentration × 100). Following SEQC ML guidelines, we determined the stability equation showing the relationship between PD variations over time by linear regression using the least squares method [1]. The model was forced to include the coordinate origin, as at time 0 loss of stability must be 0.…”

“…In our study, stability was assessed in different experimental models. In their recent guidelines for analyte stability testing, SEQC ML recommended the use of an equation or profile instead of a single stability cut-off value [1]. Based on a stability equation, laboratories can set their cut-off points according to the established specifications.…”

“…To such purpose, constituent concentrations must remain stable during the preanalytical period. The stability of biochemical analytes is defined as the ability of a sample to retain the initial value of its constituents within specified limits over a period of time under specified storage conditions [1,2]. The stability of the biological magnitudes most frequently measured in serum and plasma under specific conditions in clinical laboratories has been analyzed in numerous studies, with varying and often conflicting results.…”

“…In 2006, the Spanish Society of Laboratory Medicine (SEQC ML ) discussed this problem and developed a stability testing protocol. In 2019, a new version of the protocol was published to include a preliminary study and a complete stability test to define a stability equation [1].…”

Models to estimate biological variation components and interpretation of serial results: strengths and limitations

“…BV has a multiplicity of applications in the clinical laboratory, including internal control of the analytical process, external quality assurance programs, estimation of the reference change value (RCV) [1], verification and validation of analytical methods and as the criterion for establishing the maximum allowable deviation caused by biological sample instability [5]. BV is also used in interference studies and for establishing the limit of quantification of a measurand [6].…”