Repeated freezing and thawing of peripheral blood and DNA in suspension: effects on DNA yield and integrity.

The possibility of DNA degradation is of concern to all involved in the storage of DNA, whether for diagnostic or research purposes. Many DNA banks are at present maintained at low temperatures, but optimum conditions for storage and handling have yet to be fully assessed. Both DNA and fresh blood have been subjected to repeated cycles of freezing and thawing and DNA extracted from the blood. DNA yield has been established and integrity examined by digestion, electrophoresis, and Southern blot analysis using DNA fingerprinting techniques. No degradation of DNA could be detected using these techniques; however, DNA yield was shown to be adversely affected by freezing, with yield reduced by more than 25% in blood samples frozen only once.