In a patient who is hepatitis B surface antigen (HBsAg) positive and has a positive non‑specific syphilis screen (VDRL/RPR), how should the result be interpreted and what confirmatory testing and treatment steps are recommended?

False Positive Syphilis Non-Specific Test in HBsAg-Positive Patients

In HBsAg-positive patients with a reactive non-treponemal test (VDRL/RPR), you must perform treponemal confirmatory testing (FTA-ABS, TP-PA, or treponemal EIA/CLIA) to distinguish true syphilis infection from a false-positive result, as chronic hepatitis B infection does not appear to be a significant cause of false-positive non-treponemal tests based on current evidence.

Interpretation Algorithm

Step 1: Understand the Test Characteristics

• Non-treponemal tests (VDRL/RPR) have specificities of 87-91% in various populations, meaning false positives occur in approximately 9-13% of tests 1
• These tests are highly sensitive (97-100%) for secondary syphilis but only 62-78% sensitive for primary syphilis 1
• The literature review on false-positive non-treponemal tests examined multiple conditions including pregnancy, leprosy, drug use, malaria, HIV, hepatitis C, and autoimmune diseases 1

Step 2: Recognize the Hepatitis B Connection

Notably, hepatitis B (HBsAg positivity) is NOT listed among the conditions commonly associated with false-positive non-treponemal tests in the comprehensive guideline review 1. The guideline specifically mentions hepatitis C virus but does not identify hepatitis B as a cause of false-positive VDRL/RPR results.

Step 3: Confirmatory Testing Protocol

Regardless of HBsAg status, follow standard syphilis testing algorithms:

• If initial VDRL/RPR is reactive: Perform treponemal confirmatory testing (FTA-ABS, TP-PA, or treponemal immunoassay) 2, 3
• If treponemal test is positive: This confirms syphilis infection (current or past)
• If treponemal test is negative: The initial non-treponemal test was a false positive

The concordance between non-treponemal and treponemal tests ranges from 44-62% when using FTA-ABS as the gold standard, highlighting the necessity of confirmatory testing 2.

Step 4: Management Based on Results

If both tests are positive (confirmed syphilis):

• Stage the infection clinically and serologically
• Treat according to stage per CDC guidelines 4
• All persons with HBV infection should be tested for syphilis as part of comprehensive STI screening 4

If non-treponemal positive but treponemal negative (false positive):

• No syphilis treatment needed
• Document the false-positive result
• Consider retesting in 2-4 weeks if clinical suspicion remains high (early primary syphilis may have negative serology)

Critical Caveats

HBsAg Confirmation

For the HBsAg result itself, if the initial test shows a cutoff index (COI) between 1.0-2.0, perform neutralization confirmatory testing as 53.9% of such results may be false positives 5. This is particularly important in intermediate-prevalence populations.

Integrated Management

Since you're managing both conditions:

• Test all HBsAg-positive patients for syphilis, HIV, gonorrhea, and chlamydia per CDC guidelines 4
• Verify chronic HBV infection by retesting HBsAg and checking IgM anti-HBc 4
• Refer HBsAg-positive patients to a hepatitis specialist 4
• Vaccinate and test all sexual/household contacts of HBsAg-positive patients 4

Common Pitfall to Avoid

Do not assume the positive VDRL/RPR is false simply because the patient has hepatitis B. While various conditions cause false-positive non-treponemal tests, hepatitis B is not prominently identified as one of them in the comprehensive syphilis laboratory guidelines 1. Always confirm with treponemal testing before dismissing a reactive result.