Feasibility of Extracting Usable DNA from Blood Samples Stored up to 21 Years in the DiPiS Study

This study assesses the feasibility of extracting high-quality DNA from blood samples stored at -20°C for up to 21 years under suboptimal conditions. It addresses sample mishandling in research, where many samples lack proper biobank protocols. Prior studies focused on short-term storage and controlled conditions, highlighting the negative effects of freeze-thaw cycles. This study evaluates whether DNA from long-term stored samples under suboptimal conditions can still meet quality standards for research purposes. Genomic DNA was extracted from 1,012 capillary blood samples from the Diabetes Prediction in Skåne study. Samples were stored at -20°C for 7 to 21 years, and DNA was isolated using QIAamp DNA Blood Mini kits. DNA quantity, purity, and quality were analyzed using spectrophotometry and automated electrophoresis. Overall, 75.7% of samples met quality standards for DNA quantity (≥20 ng/µL) and purity (A260/280 ratio 1.7–1.9), with the highest proportion in 12-year samples (83.5%). DNA quality was further assessed in 270 samples, where 57.8% had a DNA Integrity Number (DIN) of 7 or higher. Despite some contamination, the majority of samples were suitable for downstream applications like next-generation sequencing. This study suggests that historical blood samples stored under suboptmal conditions can still be viable for modern genomic analyses.