False Positive Results with TB Gold Test
Yes, the TB Gold test (QuantiFERON-TB Gold) can produce false-positive results, though it has higher specificity than the tuberculin skin test (TST) for detecting Mycobacterium tuberculosis infection. 1
Causes of False-Positive Results
Cross-Reactivity with Non-Tuberculous Mycobacteria
- The TB Gold test can yield false-positive results due to cross-reactivity with certain non-tuberculous mycobacteria (NTM) 1, 2
- Specifically, cross-reactivity has been documented with:
Technical Factors
- Improper handling or processing of blood specimens can cause false-positive results 2
- Blood must be incubated with test antigens within 12 hours of collection to avoid inaccurate results 2
- Laboratory errors in sample processing or interpretation can contribute to false results
Specificity of TB Gold Test
- The TB Gold test has greater specificity than the tuberculin skin test (TST) because it uses specific M. tuberculosis antigens (ESAT-6 and CFP-10) rather than purified protein derivative (PPD) 1
- These antigens are absent from all BCG vaccine strains, which reduces false positives in BCG-vaccinated individuals 1
- Studies show that among BCG-vaccinated adults with positive TST results, only about 30% had positive QFT-G results, indicating higher specificity 4
Clinical Implications and Management
Interpreting Positive Results
- Positive TB Gold results should be interpreted in the context of:
- TB risk factors (country of origin, exposure history)
- Radiographic findings
- Clinical presentation 2
- Strong predictors of true positive QFT-G results include:
- Abnormal chest radiograph consistent with healed TB
- TST induration ≥16mm
- Birth in a high TB-incidence country 4
Recommendations for Confirmatory Testing
- For individuals at low risk for LTBI with positive QFT-G results, confirmation with TST is recommended before initiating treatment 2
- In cases of suspected false-positive results, consider:
- Repeat testing with QFT-G
- Alternative IGRA testing (such as T-SPOT.TB)
- Correlation with clinical and radiographic findings 5
Special Populations
Pediatric Considerations
- False-positive QFT-G results have been documented in children, particularly those with chronic medical conditions 6
- Data regarding false-positive rates in pediatric populations are limited, especially in low-prevalence settings 6
Healthcare Workers
- Studies have shown discordance between TST and QFT-G results in healthcare workers with multiple risk factors for LTBI 5
- Some healthcare workers with negative QFT-G results but positive TST and multiple risk factors may still have LTBI, suggesting potential false-negative QFT-G results 5
Conclusion
While the TB Gold test offers improved specificity over the TST, especially in BCG-vaccinated individuals, clinicians should be aware that false-positive results can occur due to cross-reactivity with certain NTM species and technical factors. Interpretation of results should always consider the individual's TB risk factors, clinical presentation, and radiographic findings.