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The effect of storage conditions on sample stability in the routine clinical laboratory

Background ‘Add-on’ tests are often requested for samples already in the laboratory. This study was carried out to assess the stability of common analytes in uncapped samples stored in different conditions, and therefore their suitability for ‘add-on’ requests. Methods Storage conditions evaluated included initial storage at room temperature for 16 hours, followed by storage at 4℃ (Group 1: current conditions employed in the laboratory), compared with storage at 4℃ immediately following analysis (Group 2: optimum storage conditions). Results Some analytes were not suitable for ‘add-ons’ when samples were stored in either storage condition, whereas some were suitable for ‘add-ons’ irrespective of storage condition. Storage conditions influenced the suitability of ‘add-on’ tests for a proportion of analytes including urea, amylase, total protein, alkaline phosphatase, adjusted calcium, lactate dehydrogenase, triglycerides, HDL cholesterol and total cholesterol; these analytes were stable in optimum conditions (Group 2) but not in current conditions (Group 1). Conclusions ‘Add-on’ tests can only be safely performed on a proportion of routine analytes. For some analytes, storage conditions affect their suitability for delayed analysis.