What blood tests should be done for a patient who had unprotected sex and wants to check for Sexually Transmitted Infections (STIs)?

Recommended STI Testing After Unprotected Sexual Exposure

For patients who have had unprotected sex and want to check for STIs, comprehensive testing should include blood tests for HIV, syphilis, and hepatitis B, along with nucleic acid amplification tests (NAATs) for gonorrhea and chlamydia from appropriate anatomical sites. 1

Initial Testing (At First Visit)

• Blood tests:

  • Syphilis serologic testing (nontreponemal test such as RPR or VDRL, followed by treponemal test if reactive) 1
  • HIV testing (laboratory-based Ag/Ab test) 1
  • Hepatitis B serology (especially if patient is not vaccinated) 1
  • Consider HSV-2 type-specific serology 1

• Site-specific testing for gonorrhea and chlamydia:

  • For men: urine NAAT 1
  • For women: vaginal swab (preferred), cervical swab, or urine NAAT 1
  • For patients reporting receptive anal sex: rectal NAAT for gonorrhea and chlamydia 1
  • For patients reporting receptive oral sex: pharyngeal NAAT for gonorrhea 1

• Additional testing for women:

  • Trichomoniasis: vaginal swab NAAT (preferred) or culture 1
  • Evaluate for bacterial vaginosis and yeast infection if symptomatic 1

Follow-Up Testing

• 2-week follow-up:

  • Repeat testing for gonorrhea and chlamydia if initial tests were negative, as infectious agents may not have produced sufficient concentrations to be detected at initial examination 1, 2

• 12-week follow-up:

  • Repeat serologic tests for syphilis and HIV, as these infections may take time to develop detectable antibodies 1, 2
  • If initial tests were positive, this follow-up can help determine if infection predated the exposure 1

Special Considerations

• Risk-based testing frequency:

  • Patients with high-risk factors (multiple partners, anonymous partners, substance use, previous STIs) should be screened more frequently (every 3-6 months) 1
  • Annual screening is recommended for all sexually active patients 1

• Window periods to consider:

  • HIV: 4-12 weeks for antibody development 1
  • Syphilis: 1-3 months for antibody development 1
  • Gonorrhea/Chlamydia: 1-2 weeks for adequate organism concentration 1, 2

Common Pitfalls to Avoid

• Testing too early: Testing immediately after exposure may lead to false-negative results as infections require time to develop detectable levels 2

• Incomplete anatomical site testing: Failing to test all sites of potential exposure (genital, pharyngeal, rectal) can miss infections 1

• Overlooking asymptomatic infections: Many STIs present without symptoms but can still cause complications and be transmitted 1, 3

• Assuming protection eliminates all risk: Even with partial protection, some STIs can be transmitted through skin-to-skin contact in areas not covered by barriers 2

• Neglecting follow-up testing: A single negative test shortly after exposure does not rule out infection, emphasizing the importance of follow-up testing 2

By following this comprehensive testing approach, clinicians can effectively screen for STIs in patients with recent unprotected sexual exposure, reducing the risk of complications and further transmission.