From the Guidelines
The best test for diagnosing acute tuberculosis (TB) exposure is the interferon-gamma release assay (IGRA).
Key Points
- IGRA is preferred over the tuberculin skin test (TST) for TB screening due to its better performance in diagnosing latent TB and lower interference from treatments such as glucocorticoids, DMARDs, or immunosuppressants 1.
- A chest X-ray is also recommended as part of the TB-screening procedure, especially since a negative IGRA or TST cannot exclude active TB or rule out latent TB 1.
- The concordance between different IGRAs (e.g., Quantiferon and EliSPOT) is good, and one is not recommended over the other 1.
- For individuals with a high suspicion of latent TB and/or in high-endemic countries, performing both IGRA and TST can be considered due to the low agreement between the two tests 1.
- Guidelines from various health organizations, including the WHO, USPSTF, ATS, CDC, and IDSA, support the use of IGRA over TST for diagnosing latent TB in individuals with low-to-intermediate risk of progression to active disease 1.
- It is essential to note that neither IGRA nor TST can distinguish between active and latent tuberculosis, and the diagnosis of active TB must be excluded before treating for latent TB infection 1.
From the Research
Diagnostic Tests for Acute Tuberculosis (TB) Exposure
The diagnosis of acute TB exposure is crucial for timely treatment and prevention of further transmission. Several diagnostic tests are available, each with its own advantages and limitations.
- The tuberculin skin test (TST) and interferon-γ release assays (IGRAs) are currently endorsed by the World Health Organization for detecting TB infection 2.
- IGRAs, such as QuantiFERON-TB Gold In-Tube and T-SPOT.TB, are more specific than TST but require sophisticated laboratory infrastructure and are costly to perform 2.
- New tests, including whole-blood IGRAs and skin tests using early secreted antigenic target 6 (ESAT-6) and culture filtrate protein 10 (CFP-10), have the potential to improve accuracy and operational characteristics 2.
- Molecular biology-based tests, such as real-time PCR, are highly sensitive and specific and can provide rapid diagnosis and sensitivity testing to first- and second-line drugs 3.
- Immunodiagnostic tests, including second-generation IGRAs and newer technological platforms, offer promise for ruling in or out active TB, particularly in low-burden settings 4.
Comparison of Diagnostic Tests
Studies have compared the effectiveness of different diagnostic tests for detecting TB infection.
- A systematic review of rapid diagnostic tests found that nucleic acid amplification tests (NAATs) had superior accuracy when applied to respiratory samples, but poor sensitivity when applied to other body fluids 5.
- The review also found that NAATs had high specificity for ruling in TB meningitis and pleural TB, but required combination with other tests to rule out disease 5.
- Adenosine deaminase (ADA) tests had high sensitivity for diagnosing pleural TB and TB meningitis, but limited specificity 5.
- Assays based on RD1 specific antigens, such as ESAT-6 or CFP-10, correlated better with intensity of exposure and were more likely to detect latent TB infection (LTBI) accurately than TST-based assays 5.
Limitations and Future Directions
Despite the availability of various diagnostic tests, there is still a need for improved tests that can provide high sensitivity and specificity for detecting active TB and LTBI.
- Further research is needed to establish the diagnostic accuracy of new tests in a wide spectrum of patients and to address different epidemiological and clinical settings 5.
- The development of cost-effective, accurate, and rapid diagnostic tests is crucial for controlling the spread of TB and improving patient outcomes 6, 3.