A 24-year-old woman presents to the emergency department 6 hours after alleged sexual assault. She reports vaginal pain and minimal bleeding. On examination, there are abrasions on the labia minora and posterior fourchette. The examining doctor needs to collect evidence for DNA analysis and establish proof of sexual contact. Which investigation is the investigation of choice for immediate evidence collection in this case?

Explanation

## Investigation of Choice in Acute Sexual Assault **Key Point:** High-vaginal swab (HVS) is the gold standard investigation for immediate evidence collection in alleged rape cases, particularly within 72 hours of the assault. ### Why High-Vaginal Swab? **High-Yield:** The high-vaginal swab is superior because: 1. **Semen detection** — Spermatozoa remain viable in the vagina for 48–72 hours post-assault 2. **DNA evidence** — Provides biological material for DNA profiling and comparison with suspect 3. **Acid phosphatase** — Seminal fluid marker detectable by biochemical testing 4. **Chain of custody** — Properly collected and documented for medico-legal purposes ### Timing and Technique | Aspect | Detail | |--------|--------| | **Optimal window** | Within 72 hours (ideally <24 hours) | | **Number of swabs** | Typically 2–3 swabs from different sites | | **Sites** | High vagina, cervix, rectum (if indicated), mouth | | **Preservation** | Dry swabs; air-dry before sealing in sterile container | | **Documentation** | Chain of custody form essential for court admissibility | **Clinical Pearl:** Even if spermatozoa are absent, seminal fluid markers (acid phosphatase, PSA) and non-sperm DNA from epithelial cells can still establish sexual contact and provide suspect identification. **Mnemonic — SWAB Evidence Collection:** - **S**emen and spermatozoa detection - **W**ithin 72 hours (critical window) - **A**cid phosphatase and PSA markers - **B**iological DNA for profiling ### Additional Investigations in Rape Examination While HVS is primary, the complete medico-legal examination includes: - **Genital examination** — Document injuries, abrasions, tears (as in this case) - **General body examination** — Bruises, bite marks, scratches (external evidence) - **Blood tests** — Blood group, HIV, hepatitis B/C status, pregnancy test - **Urine examination** — Toxicology if drug-facilitated assault suspected [cite:Park 26e Ch 24]