Can DNA be introduced during a medical exam?

Yes.

DNA can be introduced, moved, or redistributed during a forensic medical examination.

Vaginal swabs are routinely collected to recover biological material, but the sampling process itself can influence what is detected. Anti-contamination procedures are required because DNA can be transferred from external genital areas into internal sites during examination.

During internal sampling, swabs and instruments pass across skin surfaces and may carry biological material inward. Research has shown that DNA and sperm present externally can be introduced into vaginal swabs as part of the collection process.

Controlled forensic studies examining vaginal sampling techniques have demonstrated external-to-internal transfer in a substantial proportion of samples. In some experimental work, transfer from external genital areas was observed in around 63% of vaginal swabs collected without a speculum and in 100% of high vaginal swabs collected using a speculum.

Laboratory testing can identify DNA or sperm in a swab, but it cannot determine whether that material was deposited during the alleged event or introduced during the medical examination itself.