STI Workup for Adults
For any patient presenting with possible STI exposure, obtain site-specific nucleic acid amplification tests (NAATs) for gonorrhea and chlamydia from all exposed anatomical sites, plus blood tests for syphilis (RPR/VDRL with treponemal confirmation), HIV (Ag/Ab test), and hepatitis B serology, with mandatory follow-up testing at 2 weeks for gonorrhea/chlamydia and 12 weeks for syphilis/HIV. 1
Initial Testing Battery
Blood Tests
- Syphilis: Nontreponemal test (RPR or VDRL) followed by treponemal test if reactive 1, 2
- HIV: Laboratory-based antigen/antibody test 1, 2
- Hepatitis B: Surface antigen (HBsAg) testing, especially if unvaccinated 1, 2
Site-Specific NAAT Testing for Gonorrhea and Chlamydia
The anatomical sites tested must match the sexual exposure history 1:
- Men: Urine NAAT (first-catch urine) 1
- Women: Vaginal swab NAAT (preferred over cervical or urine) 1
- Receptive anal intercourse: Rectal NAAT for both sexes 1
- Receptive oral intercourse: Pharyngeal swab for gonorrhea (chlamydia pharyngeal testing has low yield) 3
Additional Testing for Women
- Trichomonas vaginalis: Vaginal swab NAAT (preferred) or culture 3, 1
- Bacterial vaginosis and yeast: Wet mount examination if vaginal discharge or malodor present 3
Critical Follow-Up Testing Schedule
2-Week Follow-Up
Repeat gonorrhea and chlamydia testing at all initially tested sites if initial tests were negative, as organisms may not reach detectable concentrations immediately after exposure 3, 1. This visit can be omitted if prophylactic treatment was already provided 3.
12-Week Follow-Up
Repeat serologic testing for syphilis and HIV, as antibody development requires 1-3 months for syphilis and 4-12 weeks for HIV 3, 1. Testing baseline serum collected at initial visit helps determine if infection predated the exposure 3.
Window Period Considerations
Testing too early produces false-negative results 1. Key window periods include:
- Gonorrhea/Chlamydia: 1-2 weeks for adequate organism concentration 1
- Syphilis: 1-3 months for antibody development 1
- HIV: 4-12 weeks for antibody development 1
High-Risk Patients Requiring More Frequent Screening
Patients with multiple partners, anonymous partners, substance use, or previous STIs should be screened every 3-6 months rather than annually 1. All sexually active patients warrant at least annual screening 1.
Common Pitfalls to Avoid
- Incomplete anatomical site testing: Testing only urine in men who have receptive anal intercourse misses 70% of rectal infections 1
- Single-site testing in women: Cervical-only testing misses vaginal infections 1
- Premature testing: Testing within days of exposure yields false negatives 1
- Skipping follow-up: Initial negative tests do not exclude infection 3, 1
- Overlooking asymptomatic infections: Most chlamydia and gonorrhea infections are asymptomatic but cause complications and ongoing transmission 1, 4
Special Populations
Sexual Assault Cases
The workup differs slightly for assault cases 3:
- Collect specimens from all sites of penetration or attempted penetration 3
- Preserve baseline serum for comparison with follow-up tests 3
- Consider empiric prophylaxis: ceftriaxone 125 mg IM + metronidazole 2 g PO + doxycycline 100 mg PO twice daily for 7 days 3
- Offer hepatitis B vaccination 3
Children
In suspected sexual abuse cases, use only culture-based methods (not NAATs) for gonorrhea and chlamydia due to legal implications, with confirmation by two different testing principles 3. Test pharynx, anus, vagina (girls), and urethra (boys) 3.