SLE and False Positive Mantoux Test
No, SLE does not cause false positive Mantoux (tuberculin skin test) results—it causes false negative results due to immunosuppression. 1
Understanding the Relationship Between SLE and Tuberculin Testing
False Negative Results in SLE
The American Thoracic Society and CDC explicitly list diseases affecting lymphoid organs, including systemic lupus erythematosus, as causes of false negative tuberculin skin test results, not false positive. 1 This occurs through several mechanisms:
- Disease-related immunosuppression: SLE itself causes nonspecific immunosuppression that can suppress the PPD response 1
- Medication effects: Corticosteroids and immunosuppressive agents commonly used in SLE treatment further suppress tuberculin reactivity 1
- Lymphoid organ dysfunction: SLE affects lymphoid organs, impairing the delayed-type hypersensitivity response required for a positive Mantoux test 1
False Positive Results: Different Mechanisms
False positive tuberculin tests occur from entirely different causes unrelated to SLE 1:
- Cross-reactivity with non-tuberculous mycobacteria (environmental mycobacteria exposure) 1
- Prior BCG vaccination 1
- Product-related problems with specific PPD lots 2
Clinical Implications for SLE Patients
TB screening remains critical in SLE patients despite the risk of false negatives. 3 The American College of Rheumatology recommends TB testing before starting glucocorticoids and immunosuppressive drugs in SLE patients, particularly in endemic areas where TB frequency reaches 2.5-13.8% in SLE populations. 3
Recommended Screening Approach:
- Use interferon-gamma release assays (IGRA) in addition to tuberculin skin testing, especially in BCG-vaccinated individuals 1
- Consider booster TST 1-2 weeks after initial negative test in patients on immunomodulators, as this identifies an additional 8-14% of latent TB cases 1
- Any induration ≥5 mm should be considered positive for latent TB in immunosuppressed patients 1
- IGRA tests are preferred as they complement TST and avoid BCG cross-reactivity 1
Common Pitfall to Avoid
The critical error is assuming a negative Mantoux test rules out TB in SLE patients. 4 A negative test may represent false negative results from immunosuppression rather than true absence of infection. 1 When clinical suspicion for TB exists despite negative testing, proceed with chest radiography and consider IGRA testing. 1
Confusion with Other False Positive Tests
SLE patients do experience false positive results with different serologic tests, particularly HIV testing 5, 6, but this phenomenon does not extend to the Mantoux test, which shows the opposite pattern of false negativity. 1