Diagnostic Methods for Childhood Tuberculosis
Tuberculin Skin Test (TST) and Interferon-Gamma Release Assays (IGRA)
Tuberculin Skin Test (TST) and Interferon-Gamma Release Assays (IGRA) are key diagnostic methods for detecting childhood tuberculosis. IGRA is more specific than TST, but accessibility and cost remain challenges.
Diagnostic Methods for Childhood Tuberculosis
Tuberculin Skin Test (TST) and Interferon-Gamma Release Assays (IGRA)
Childhood tuberculosis (TB) remains a major public health concern, requiring accurate diagnostic methods for early detection and treatment. Two primary methods used for diagnosing latent tuberculosis infection (LTBI) and active TB in children are the Tuberculin Skin Test (TST) and Interferon-Gamma Release Assays (IGRA).
Tuberculin Skin Test (TST)
The Tuberculin Skin Test (TST), also known as the Mantoux test, is a traditional method for detecting TB infection. It involves intradermal injection of purified protein derivative (PPD) and evaluating the skin's reaction after 48-72 hours.
- Procedure: A small amount of PPD is injected into the skin on the forearm.
- Interpretation: The reaction is measured in millimeters of induration (raised, hardened area). A positive result may indicate prior exposure to Mycobacterium tuberculosis.
- Limitations: False positives can occur due to Bacillus Calmette-Guérin (BCG) vaccination or environmental mycobacteria exposure.
Interferon-Gamma Release Assays (IGRA)
Interferon-Gamma Release Assays (IGRA) are blood-based tests that measure the release of interferon-gamma (IFN-γ) in response to TB-specific antigens.
- Types: The two main IGRA tests are QuantiFERON-TB Gold (QFT) and T-SPOT.TB.
- Procedure: A blood sample is drawn and incubated with TB-specific antigens. The level of IFN-γ released is then measured.
- Advantages: IGRA tests do not cross-react with BCG vaccination, making them more specific than TST.
- Limitations: Higher cost and need for laboratory infrastructure can limit accessibility.
Comparison of TST and IGRA
| Feature | TST | IGRA |
|---|---|---|
| Sample Type | Skin injection | Blood sample |
| Result Time | 48-72 hours | Within 24 hours |
| BCG Interference | Possible | None |
| Cost | Lower | Higher |
Conclusion
Both TST and IGRA are useful for detecting childhood tuberculosis, but IGRA offers higher specificity. The choice of test depends on individual risk factors, healthcare settings, and available resources.
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