Evaluating the utility of storage solutions to preserve nucleic acid integrity at ambient temperature in South Africa

Abstract

Background: Maintaining nucleic acid integrity during transport and storage is important for downstream diagnostic and research applications. Innovative solutions are needed to reduce the requirement for costly cryopreservation in low- and middle-income countries. Objective: To assess the feasibility of nucleic acid storage at a range of temperatures using commercially available storage solutions and as dried blood spots (DBS). Methods: Total nucleic acids were extracted from 50 residual blood samples sourced from a routine haematology laboratory in Johannesburg, South Africa between 01 March 2021 and 15 December 2023. DNA and RNA aliquots were stored in commercial storage media and as DBS at a range of temperatures (-80 °C, 2 °C - 8 °C, room temperature [RT] and 40 °C - 50 °C) for 24 h, 96 h, 30 days and 90 days. Post-storage nucleic acid concentration and integrity were measured. Results: Four DNA and four RNA aliquots (stored complexed to beads and in commercial storage solution) and three DBS prepared from 50 whole blood samples were analysed. Nucleic acids stored at RT and at 2 °C - 8 °C maintained acceptable concentration and integrity tested using TapeStation Bioanalyser with a DNA integrity number median score of 7.5 (RT) and 7.4 (2 °C - 8 °C) for both beads and storage solutions, and DNA integrity number (acceptable range above 7). RNA integrity was moderate, with a median RNA integrity range of 3.1-3.9 (acceptable range above 5). Samples stored at 40 °C - 50 °C showed extensive degradation with no bands produced on gel electrophoresis. Dried blood spot yielded low RNA concentrations (median 1.33 ng/μL, range 0.08 - 4.63 ng/μL). Conclusion: Commercial storage solutions, beads and DBS offer a feasible alternative to cryopreservation for the storage of nucleic acids at ambient temperature. What this study adds: This study is a proof-of-concept study which investigates the feasibility of nucleic acid storage and transport at RT in Africa.