Abstract Objectives This stability study aimed to evaluate the stability of 48 biochemical analytes in pooled serum samples derived from leftover sera over 14 days at room temperature (RT) and at 2–10 °C, and to assess the consistency of storage effects across independent pools. The goal was to determine the suitability of such materials for external quality assessment (EQA) schemes. Methods A total of 110 residual serum samples were derived from Greiner Bio-One Vacuette tubes (with or without separator gel) and randomly assigned to 10 pools. Aliquots were stored at RT or 2–10 °C and analysed on days 0, 1, 2, 3, 4, 7, and 14 using Roche Cobas and DiaSorin Liaison platforms. Percent deviations from baseline (PD%) were compared against maximum permissible differences (MPDs) derived from reference change values. Inter-pool variability was assessed by linear regression of standard deviations of PD%-values over storage time. Results Under refrigerated conditions, six analytes exceeded stability limits, with only alanine aminotransferase (ALAT), lactate dehydrogenase (LDH), and 1,25(OH) 2 vitamin D showing instability within seven days and the others not before day 14. At RT, 38/48 parameters remained stable for at least 4 days. Inter-pool variability increased significantly for only three parameters at 2–10 °C and nine at RT, with most slopes below 0.35 %/day, indicating largely matrix-independent degradation patterns. Conclusions The majority of analytes in pooled leftover sera demonstrated acceptable stability, particularly under refrigerated conditions. Storage effects occurred consistently across pools, supporting reproducibility. These findings indicate that pooled sera from diagnostic leftovers represent a practical resource for EQA when analysed within defined timeframes.
Zabel et al. (Thu,) studied this question.