What is the initial Hepatitis B (HB) test to order for a patient with Sexually Transmitted Infection (STI) concerns?

Initial Hepatitis B Testing for STI Concerns

Order hepatitis B surface antigen (HBsAg) as the initial screening test for patients with sexually transmitted infection concerns. 1

Primary Screening Approach

The CDC STI Treatment Guidelines establish that HBsAg is the primary marker for detecting active HBV infection (both acute and chronic) in patients presenting with STI concerns. 1, 2 This single test identifies patients who are currently infected and potentially infectious to sexual partners, which is the most critical clinical determination in the STI setting. 1

Why HBsAg First

• HBsAg detects active infection requiring immediate public health intervention, partner notification, and clinical management. 1
• Patients with positive HBsAg must be reported to state/local health departments and require further evaluation for chronic infection. 1
• Sexual partners of HBsAg-positive patients need urgent postexposure prophylaxis (HBIG plus vaccine) within 14 days of last sexual contact. 1

Comprehensive Three-Test Panel (Preferred When Resources Allow)

For complete assessment of HBV status, order all three tests simultaneously: 3

1. HBsAg (hepatitis B surface antigen) - detects current infection 1, 3
2. Anti-HBc (total hepatitis B core antibody) - detects past or current infection 1, 3
3. Anti-HBs (hepatitis B surface antibody) - detects immunity from vaccination or resolved infection 1, 3

The 2023 CDC screening recommendations advocate for this three-test approach for all adults ≥18 years at least once in their lifetime, which includes patients presenting with STI concerns. 3

Clinical Context for STI Patients

Hepatitis B has strong epidemiologic association with STIs. 4 Patients with current or past STIs demonstrate:

• HBsAg prevalence of 4.17% (median across studies), significantly elevated compared to general population 4
• Prevalence ratios ranging from 1.65 to 6.76 for HBsAg positivity when STI history present 4

All persons with HBV infection should be tested for HIV, syphilis, gonorrhea, and chlamydia given the overlapping transmission routes and risk behaviors. 1

Interpretation Algorithm

If HBsAg Positive:

• Add IgM anti-HBc to distinguish acute from chronic infection 1, 2
• IgM anti-HBc positive = acute hepatitis B 1, 2
• IgM anti-HBc negative = chronic hepatitis B 1, 2
• Initiate partner notification and postexposure prophylaxis for sexual contacts within 14 days 1
• Report to health department 1
• Refer to specialist if chronic infection confirmed 1

If HBsAg Negative but Anti-HBc Positive:

• Check anti-HBs to determine if resolved infection (anti-HBs positive) or potential occult infection (anti-HBs negative) 1
• Isolated anti-HBc may indicate past infection, chronic low-level infection, or false positive 1

If All Tests Negative:

• Offer hepatitis B vaccination series if not previously vaccinated 1
• Vaccination is critical for STI clinic populations given ongoing high-risk behaviors 1

Critical Pitfalls to Avoid

Do not order only anti-HBs or anti-HBc without HBsAg in the initial STI evaluation, as this misses active infections requiring immediate intervention. 1, 5

Do not delay testing for HBsAg while obtaining detailed sexual history, as the test should be performed regardless of disclosed risk factors. 3

Do not use IgM anti-HBc as initial screening test - it has low positive predictive value in asymptomatic persons and should only be added when HBsAg is positive or acute hepatitis is clinically suspected. 2

Remember that rapid point-of-care HBsAg tests have excellent sensitivity (98.3%-99.3%) and specificity (98.0%-99.5%), making them suitable for immediate screening in STI clinic settings. 6