Biochemical analytes stability in refrigerated (2–8°C) and frozen (−20°C) serum samples at Kericho County Hospital Laboratory, Kenya

Abstract

Pre-analytical variables, including samples storage, can adversely affect the reliability of medical laboratory results. Add-on tests, alongside unprecedented delays in testing, require that samples are stored in a manner that maintain their integrity and optimally preserve the various analytes. Refrigeration and freezing, are well-documented preservation methods used by medical laboratories for short and long term storage of retained specimen. Different analytes however vary considerably in stability when samples are stored over a period of time. This study aimed at evaluated the stability of selected biochemical analytes in refrigerated (2 – 8^oC) and frozen (-20^oC) serum, to determine the maximum storage period at which accurate and reliable results can still be obtained at the Kericho County Hospital laboratory, guiding specific analytes delayed and add-on testing storage requirement and timelines. Samples drawn from twenty healthy volunteering adult participants, randomly picked from the local population, were processed and analysed at baseline, then a set of aliquots refrigerated and another frozen, in batches marked for analysis on the 7^th, 14^th, 21^st and 28^th days, on a well maintained, accurately calibrated, and quality checked HumaStar 100, an automated biochemistry analyser. Fridge and freezer temperatures were maintained relatively constant at 2 – 8^oC and -20^oC respectively, with routine monitoring throughout the period. The data was coded and analysed on SPSS version 22. The statistical significance of the difference in the determined analyte concentrations in comparison to baseline levels was evaluated using student paired T-test and Wilcoxon rank test. From the findings, alkaline phosphate, creatinine, and aspartate aminotransferase were found to be stable up to 28 days in the refrigerated and frozen serum, with mean percentage differences less than calculated reference change value of 16.48, 35.97 and 42.25 respectively. Sodium, total and direct bilirubin, were however unstable, as their mean percentage difference was more than the calculated reference change value of 2.16, 0.657 and 1.14. Urea and glucose showed stability at 2-8℃ for up to the 14^th day, while potassium and chloride were only stable in refrigerated serum up to the 7^th day analysis. Freezing improved the stability of all the analytes except bilirubin, ALT and sodium. This study recommends immediate analysis of serum for sodium, bilirubin, and ALT, which should never be part of add-on tests, and freezing of the samples when analysis is delayed for the other analytes.