Evaluation of the short-term stability of specimens for clinical laboratory testing

A major concern in both the laboratory-medicine and research communities is the quality of human specimens for analysis. However, there is insufficient scientific evidence regarding optimal conditions for handling and storing routine specimens, especially those in liquid form. Thus, we investigated the stability of clinically relevant samples stored under various conditions.

Ten clinical laboratories in Japan conducted analyses of the stability of post-clinical (left over after analysis) test samples in relation to temperature and storage duration. We examined serum, whole blood, and urine samples submitted to each laboratory for routine testing. In this study, at least 5 samples for each of 35 tests were analyzed at each laboratory. After completion of routine testing, specimens with sufficient residual volume and values between LL-R/2 (lower limit of reference interval) and UL+R/2 (upper limit) were divided into 300 μL aliquots, where R=UL - LL. Aliquots of serum specimens were stored at either room temperature (23°C), 4°C, -20°C, or -80°C without light exposure. Aliquots of whole blood and urine specimens were stored at either 23°C or 4°C. The storage time was either 1, 3, or 7 days. Average differences between pre- and post-storage test results were evaluated for each laboratory test by two-way ANOVA. F-values for between-day variations were used for judging the statistical significance of storage-related changes in test values, whereas the ratio of between-day SD to between-individual SD (one-fourth of reference interval) was used to indicate the practical significance of the change.

Sample denaturation is clearly temperature- and storage-duration dependent for almost all analytes. In general, specimens were most susceptible to denaturation at 23°C, then 4°C, -20°C, and -80°C. This study confirmed the accumulated routine, practice-based, detailed knowledge regarding specimen stability and will help to ensure the reliability of laboratory test results.