Effect of multiple freezing and thawing of serum on TT virus and hepatitis B virus DNA positivity

This study was done to determine the effect of freezing and thawing of serum on the stability of TTV and HBV DNA levels. Seven TTV DNA positive samples were randomly selected among the sera having HBV DNA with concentrations ranging from 12 pg/ml to 4162 pg/ml and they were frozen and thawed up to eight times and then analyzed for changes on TTV- and HBV DNA levels. TTV DNA positivity and HBV DNA concentrations were tested by using semi-nested PCR and Digene hybrid capture system, respectively. Seven cycles of freezing and thawing did not significantly change HBV DNA concentrations and TTV DNA positivity in any of the samples tested. After eight cycles, only three samples were tested, and all were positive for HBV DNA, but negative for TTV DNA. Our results show that both TTV- and HBV DNA positives continued until the seventh cycle of freezing and thawing in all samples tested.