DNA extraction from bloodstains in respect to age and stained substrate

The amount and the quality of DNA that could be extracted from bloodstains equivalent to 200 microliters blood were examined after 3, 6, 9, 12, 15, 18 and 21 days of storage under dry or humid conditions at room temperature. DNA was also extracted from two days old 200 microliters bloodstains on different stain carriers. The amount of DNA that could be extracted showed a dependency on all the parameters that were examined. On carriers with a rough surface structure, where the blood can soak in, the resolving of leukocytes was impaired and the DNA recovery rate was low, e.g. carpeting and suede. The DNA yield was higher for substrates with a smooth surface, e.g. paper, glass and smooth leather. The aging experiments revealed that for the stains stored under dry conditions, there was no decrease in the DNA yield for stains on glass, while the amount of DNA that could be extracted became less for older stains on cotton. Under humid conditions the DNA yield was high and did not decrease for both glass and cotton fabric. The quality of the DNA was not impaired by aging or storage conditions, but for several stain carriers the DNA was contaminated by chemical substances which inhibited restriction enzyme digestion and successful DNA-typing.