From the Guidelines
A change from a negative to positive QuantiFERON-TB Gold test (IGRA) indicates you have likely been infected with tuberculosis (TB) bacteria since your last test, and you should contact your healthcare provider immediately for evaluation. This conversion could be due to recent TB exposure, progression from a previously undetectable infection, or immune system changes allowing detection of an existing infection 1. False positives can occur from laboratory error, cross-reactivity with non-tuberculous mycobacteria, or recent BCG vaccination, though the latter is less common with QuantiFERON tests than with skin tests.
Possible Causes of Conversion
- Recent TB exposure: This is a high-risk scenario, especially if you have been in close contact with someone with active TB disease 2.
- Progression from a previously undetectable infection: This could be due to changes in your immune system or the progression of the infection itself.
- Immune system changes: Certain medical conditions or treatments can affect your immune system, making it more likely to detect an existing infection.
Next Steps
You should undergo a medical evaluation, which typically includes:
- A chest X-ray to rule out active TB disease
- A physical examination and medical history to identify any risk factors or symptoms
- Bacteriologic studies and serology for human immunodeficiency virus (HIV) if indicated 1 If active TB is excluded, you may be diagnosed with latent TB infection (LTBI) and offered preventive treatment, usually isoniazid (300mg daily for adults) for 6-9 months, rifampin (600mg daily for adults) for 4 months, or a 3-month regimen of weekly isoniazid plus rifapentine. Treatment reduces your risk of developing active TB disease by 60-90% 2.
Important Considerations
- The decision to treat depends on your risk factors, including immune status, age, and potential exposure history.
- Certain groups, such as close contacts of persons with infectious pulmonary TB, persons who have immigrated from areas with high rates of TB, and children under 5 years old, are at higher risk for recent TB infection and progression to active disease 2.
From the Research
Possible Causes of Reversion in QuantiFERON Test Results
The reversion from a negative to a positive QuantiFERON test result can be attributed to several factors. Some possible causes include:
- Recent exposure to tuberculosis (TB) 3
- Waning immunity over time, leading to a reactivation of latent TB infection 3
- Variability in test results due to factors such as the timing of the test, the individual's immune response, and the presence of other infections 3
Risk Factors for Reversion
Certain risk factors can increase the likelihood of reversion in QuantiFERON test results. These include:
Treatment and Prevention of Latent TB Infection
Treatment of latent TB infection (LTBI) is crucial in preventing the progression to active TB disease. Various treatment regimens are available, including:
- Isoniazid monotherapy for 6-9 months 4, 5, 6, 7
- Rifampin-based regimens, such as once-weekly isoniazid and rifapentine for 12 weeks 4, 5, 6, 7
- Four months of rifampin, which has been shown to be effective and does not require directly observed therapy (DOT) 7
Serial Testing and LTBI Treatment
Serial testing without LTBI treatment may be indicated in certain individuals, such as those who are female, younger, and have lower QuantiFERON test results 3. However, the decision to treat or not treat LTBI should be made on a case-by-case basis, taking into account individual risk factors and medical history.