From the Guidelines
The recommended method for tuberculosis (TB) screening is the interferon-gamma release assay (IGRA) blood test, which is preferred over the tuberculin skin test (TST) due to its higher specificity and lower false-positive results, especially in individuals with a history of BCG vaccination or immunosuppression. The IGRA blood tests, such as QuantiFERON-TB Gold or T-SPOT.TB, measure the immune response to TB antigens and can provide results within 8 to 30 hours 1.
Key Considerations for TB Screening
- The TST involves injecting a small amount of purified protein derivative (PPD) under the skin, with results read 48-72 hours later by measuring induration at the injection site.
- IGRA is preferred for people who have received BCG vaccination since it does not cross-react with the vaccine.
- For individuals with positive screening tests, follow-up evaluation should include a chest X-ray and symptom assessment to rule out active TB disease.
- High-risk groups requiring regular screening include healthcare workers, immunocompromised individuals, close contacts of TB patients, and those from countries with high TB prevalence.
Screening Approach
The screening approach works by detecting either a delayed-type hypersensitivity reaction to TB antigens (TST) or by measuring T-cell release of interferon-gamma in response to TB antigens (IGRA), both indicating TB infection rather than necessarily active disease 1.
Recent Guidelines
Recent guidelines from 2023 recommend using IGRA over TST for TB screening, especially in individuals with low-to-intermediate risk of progression to active disease, due to its higher specificity and lower false-positive results 1. However, in cases of high suspicion for latent TB or in high-endemic countries, performing both tests can be considered.
Test Selection
The selection of the most suitable test or combination of tests for detection of M. tuberculosis infection should be made on the basis of the reasons and the context for testing, test availability, and overall cost-effectiveness of testing 1.
Recommendations for High-Risk Groups
Systematic testing and treatment of latent tuberculosis infection (LTBI) should be performed in people living with HIV, adult and child contacts of pulmonary TB cases, patients initiating anti-tumour necrosis factor treatment, patients receiving dialysis, patients preparing for organ or haematological transplantation, and patients with silicosis, using either IGRA or TST 1.
From the FDA Drug Label
Before isoniazid preventive therapy is initiated, bacteriologically positive or radiographically progressive tuberculosis must be excluded. Appropriate evaluations should be performed if Extra pulmonary tuberculosis is suspected.
The recommended method for Tuberculosis (TB) screening is not explicitly stated in the provided drug label. However, it mentions that bacteriologically positive or radiographically progressive tuberculosis must be excluded before initiating isoniazid preventive therapy, and appropriate evaluations should be performed if Extra pulmonary tuberculosis is suspected.
- Key points:
- Bacteriologic evaluation
- Radiographic findings
- No specific TB screen test is mentioned in the label 2.
From the Research
Tuberculosis Screening Methods
The recommended method for tuberculosis (TB) screening includes:
- Tuberculin skin test (TST)
- Interferon-gamma release assays (IGRAs) such as T-SPOT.TB and QuantiFERON-TB Gold In-Tube (QFT-GIT) 3, 4, 5, 6, 7
Comparison of TST and IGRA
- IGRAs, especially T-SPOT.TB, are more effective at detecting TB infection than TST 3
- T-SPOT.TB was significantly more sensitive than TST, with a sensitivity of 90% compared to 64% for TST 3
- QFT-GIT seemed to be more sensitive than TST, but similarly specific 3
- IGRA has a better predictive ability than TST for the progression of latent infection to active tuberculosis disease 6
Limitations and Considerations
- Both TST and IGRA have limitations, including spontaneous variability and lack of a validated definition of conversion and reversion, making it difficult for clinicians to interpret changes in category (conversions and reversions) 5
- TST conversion alone may overestimate Mtb infection, and its correlation to older age suggests an "environmental" boosting response due to prolonged exposure to environmental mycobacteria 7
- Dual testing with TST and IGRA may improve detection, but further confirmation is needed 6