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Objectives In clinical laboratories it is necessary to know for how long the analytes are stable in the samples with specific storage conditions. Our laboratory has implemented the new Aptio Automation System (AAS) (Siemens Healthcare Diagnostics) where the analyzed samples are stored in a refrigerated storage module (RSM) after being sealed. The aim of the study was to evaluate the stability of serum samples with the AAS and comparing the results with a previous study using a conventional refrigerated system. Design and methods Serum samples from a total of 50 patients were collected and for each of them 27 biochemical analytes were analyzed. The samples were divided in 5 sets of 10 samples. Each set was re-analyzed at one of the following times: 24, 48, 72, 96 and 120 h. Stability was evaluated according to the Total Limit of Change (TLC) criteria, which combine both analytical and biologic variation. Results A total of 26 out of 27 analytes were stable at the end of the study according to TLC criteria. Lactate dehydrogenase was not stable at 48 h observing a decrease in its concentration until the end of the study. In the previous study (conventional storage system) 9 biochemical analytes were not stable with an increase of their levels due to the evaporation process. Conclusions The RSM connected to the AAS improves the stability of serum samples. This system avoids the evaporation process due to the sealing of samples and allows better control of the samples during their storage. [ABSTRACT FROM AUTHOR]