What blood and urine tests are recommended for comprehensive STI (Sexually Transmitted Infection) screening?

Comprehensive STI Screening: Blood and Urine Tests

For comprehensive STI screening, order blood tests for syphilis (both nontreponemal RPR/VDRL and treponemal EIA/CIA) and HIV (laboratory-based antigen-antibody test), plus urine nucleic acid amplification tests (NAATs) for gonorrhea and chlamydia, with additional site-specific testing based on sexual practices. 1

Core Blood Tests for All Patients

Syphilis Screening

• Nontreponemal test: RPR (Rapid Plasma Reagin) or VDRL (Venereal Disease Research Laboratory) 1
• Treponemal test: EIA (Enzyme Immunoassay) or CIA (Chemiluminescent Immunoassay) 1
• Both tests are required for diagnosis—a single positive test is insufficient 1
• Repeat testing at 6-12 weeks if initial test is negative but exposure occurred recently 2

HIV Testing

• Laboratory-based antigen-antibody test (4th generation) 1
• HIV RNA test if available, particularly for recent exposures 1
• Follow-up testing at 4-6 weeks post-exposure is critical due to the window period 2
• Definitive testing at 12 weeks (3 months) after exposure 2

Hepatitis B Serology

• Baseline serologic testing for hepatitis B if not previously vaccinated 1, 2

HSV-2 Serology (Optional)

• Type-specific glycoprotein G-based serology can be considered for patients who wish to know their HSV-2 status 1

Urine Tests

Gonorrhea and Chlamydia

• Urine NAAT for both gonorrhea and chlamydia in men 1
• Urine NAAT is acceptable for women, though vaginal swabs are preferred 1
• NAATs have superior sensitivity compared to culture, particularly for chlamydia 1

Critical caveat: Urine-only testing misses the majority of infections in men who have sex with men and individuals with receptive anal or oral sex exposure 2, 3. Testing only urogenital sites detects as few as 63% of infections 4.

Additional Site-Specific Testing Based on Sexual Practices

For Receptive Anal Sex

• Rectal NAAT for both gonorrhea and chlamydia 1, 3
• Rectal specimens are essential—66% of chlamydia and 55% of gonorrhea infections in MSM occur at the anorectal site 5
• Use validated NAATs at laboratories that have met CLIA requirements 1

For Receptive Oral Sex

• Pharyngeal NAAT or culture for gonorrhea 1, 3
• Pharyngeal testing detects 47% of chlamydia and 61% of gonorrhea infections in MSM 5
• Pharyngeal chlamydia screening is generally not recommended for routine screening 1

For Women

• Vaginal swab NAAT (preferred over urine or cervical swab) for gonorrhea and chlamydia 1
• Vaginal swab NAAT for trichomonas 1, 2
• Vaginal swabs detect 86% of infections compared to only 63% for urine 4

Screening Frequency and Timing

Initial Screening

• Perform comprehensive testing at baseline, including all exposure-specific sites 1, 2
• Bacterial STIs (gonorrhea, chlamydia) can be detected even within 72 hours of exposure using NAATs 2

Follow-Up at 3 Months

• Mandatory repeat testing for HIV and syphilis due to window periods 2
• Retest for gonorrhea and chlamydia if initially positive and treated, due to 25% reinfection rates within 3-4 months 2

Ongoing Screening for High-Risk Individuals

• Every 3-6 months for patients with multiple or anonymous partners, substance use during sex, history of STIs, or MSM 1, 2
• Annual screening minimum for all sexually active patients 1

Common Pitfalls to Avoid

1. Single-site testing in MSM: Testing only urine misses 34-45% of infections 4, 5. Always perform three-site testing (urogenital, rectal, pharyngeal) 3.

2. Relying on symptoms: Most STIs are asymptomatic (74-81% of cases), making laboratory screening essential 1.

3. Single HIV test after exposure: The window period requires follow-up testing at 4-6 weeks and definitive testing at 12 weeks 2.

4. Inadequate syphilis testing: Both treponemal and nontreponemal tests are required for diagnosis 1.

5. Skipping trichomonas testing in women: Use vaginal NAAT, not Pap smear, which has poor sensitivity 1, 2.