In a case of alleged sexual assault, vaginal/rectal swabs are collected 60 hours post-assault. Spermatozoa are not found. The BEST specimen to maximise probability of DNA recovery from the assailant at this time point is:

• A High vaginal swab for sperm
• B Cervical mucus swab, as spermatozoa may survive in cervical crypts for up to 5 days
• C Urine sample for prostatic acid phosphatase
• D Skin swabs from bite marks and areas of body contact (neck, breast, wrist) for touch/salivary DNA ✓

Explanation

At 60 hours post-assault, vaginal spermatozoa have usually been eliminated by vaginal flora and immune mechanisms; the window for vaginal swab recovery is approximately 72 hours (motile sperm disappear earlier). Cervical crypts can retain sperm for up to 5 days but are less reliable at 60 hours. The most productive alternative is skin swabs from bite marks, body contact areas, and lick sites, which contain salivary DNA (buccal epithelial cells) with a much longer persistence on skin. Urine prostatic acid phosphatase is unreliable and non-specific at 60 hours.

Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.