What lab tests are recommended for diagnosing sexually transmitted infections (STIs)?

Recommended Laboratory Tests for Diagnosing Sexually Transmitted Infections

Comprehensive STI screening should include nucleic acid amplification tests (NAATs) for chlamydia, gonorrhea, and trichomonas, serologic testing for syphilis and HIV, and appropriate site-specific testing based on sexual practices. 1

Core STI Diagnostic Tests

1. Bacterial STI Testing

• Chlamydia and Gonorrhea:

  • NAAT testing is the gold standard with highest sensitivity (86.1%-100%) and specificity (97.1%-100%) 1, 2
  • Specimen types:
    • Urine-based NAATs (first-void urine) for all patients
    • Vaginal/cervical swabs for women
    • Extragenital site testing (rectal, oropharyngeal) is essential for high-risk individuals, particularly MSM 1, 3
  • Culture for gonorrhea is indicated when antimicrobial susceptibility testing is needed (treatment failures) 1

• Syphilis:

  • Serologic testing is the standard approach 1
  • Most laboratories use reverse screening algorithm:
    • Treponemal-specific test first (EIA/chemiluminescence immunoassay)
    • Followed by nontreponemal test (RPR) to confirm 1
  • All patients with genital lesions should receive syphilis testing 1

• Mycoplasma genitalium:

  • Emerging pathogen causing nongonococcal urethritis and PID
  • NAAT testing when available 1, 2

2. Viral STI Testing

• HIV:

  • Serologic screening recommended for all patients seeking STI evaluation 1
  • Particularly important for pregnant women and high-risk individuals 1

• Herpes Simplex Virus (HSV):

  • For genital lesions: NAAT, viral culture, or DFA testing 1
  • NAATs are most sensitive, especially for non-ulcerative or vesicular lesions 1
  • Type-specific testing (HSV-1 vs HSV-2) is important 1

• Hepatitis B:

  • Serologic testing for hepatitis B surface antigen (HBsAg) 1
  • Particularly important in pregnant women 1

• Hepatitis C:

  • Consider screening in MSM due to emerging sexual transmission 1

3. Parasitic STI Testing

• Trichomonas vaginalis:
  • NAAT testing is recommended, particularly in women 1, 4
  • Can be included in multiplex STI panels 1

Population-Specific Testing Recommendations

For Women

• Comprehensive testing should include:
  • Cervical/vaginal specimens for chlamydia, gonorrhea, and trichomonas
  • Serologic testing for syphilis and HIV
  • Consider testing for bacterial vaginosis and vulvovaginal candidiasis 1, 4

For Pregnant Women

• Required screening tests:
  • Serologic test for syphilis (early pregnancy and possibly third trimester)
  • Serologic test for hepatitis B surface antigen
  • Tests for gonorrhea and chlamydia
  • HIV testing 1

For Men Who Have Sex with Men (MSM)

• Critical to test multiple anatomic sites:
  • Urethral/urine specimens
  • Rectal swabs for gonorrhea and chlamydia
  • Pharyngeal swabs for gonorrhea 1, 3
• More comprehensive HIV, syphilis, and hepatitis testing 3

Important Clinical Considerations

Specimen Collection

• Self-collected or provider-collected vaginal swabs are acceptable and highly sensitive 4
• Proper technique is essential to prevent inadequate specimen collection 3
• First-void urine (first 20-30 mL) is optimal for urethral infections 1

Multiplex Testing

• Simultaneous testing for multiple STIs (chlamydia, gonorrhea, trichomonas) is optimal for detection of the most common treatable STIs 1
• Multiplex PCR panels can improve efficiency when available 3

Common Pitfalls to Avoid

1. Testing only urogenital sites in MSM and other high-risk individuals - can miss 25-40% of infections 1, 3
2. Relying on symptoms - most STIs are asymptomatic (70% of HSV and trichomoniasis, 53-100% of extragenital gonorrhea and chlamydia) 2
3. Failing to screen partners - reinfection from untreated partners is common (25-40% of treatment "failures") 1
4. Not considering antimicrobial resistance - particularly for gonorrhea and M. genitalium 1, 2

Remember that positive tests for chlamydia, gonorrhea, syphilis, chancroid, and HIV require reporting to public health authorities according to local requirements 1.