The effects of storage of blood and isolated DNA on the integrity of DNA

Long-term storage of DNA is required for a number of genetic studies; prior to extraction, blood samples may be subject to elevated temperatures for variable intervals. We have studied the effect of temperatures ranging from −70°C to +65°C on human blood and on DNA extracted from it. DNA in solution stored at ambient temperatures up to 37°C for 6 months was digestible by three different restriction endonucleases, whereas storage at 45°C is deleterious after 6-7 weeks. DNA can be extracted from blood samples stored at −70°C for at least 2 months or at 23°C for a week or more, but blood stored at these temperatures may yield less high-molecular-weight DNA. Cell pellets from which plasma has been removed also can serve as a source of DNA. Isolated DNA stored dry for years (up to 30) is difficult to dissolve and may appear degraded, but a sample stored dry for 13 years and then in solution at −20°C for 7 years appeared to be intact.