Quantiferon TB Gold / Interferon Gamma release assay (IGRA)

Key Features of the QFT-Plus Test

• Methodology: A blood sample is mixed with TB-specific antigens, and the level of interferon-gamma (IFN-γ) produced by T-cells is measured.
• Advantages:
  • Single Visit: No return visit required (unlike the TB skin test/TST).
  • BCG Unaffected: Results are not affected by prior BCG vaccination.
  • Rapid Results: Results are generally available within 24–48 hours.
  • High Sensitivity: Accurate in detecting infection, particularly in people at risk of infection.
• Limitations:
  • Cannot Differentiate: It cannot distinguish between latent TB infection (LTBI) and active TB disease on its own.
  • Indeterminate Results: Can occur in immunocompromised patients.
  • Age Restriction: Not typically recommended for children under 5 years old.

Results Interpretation

• Negative: No TB infection detected.
• Positive: Likely indicates a TB infection (latent or active). Further testing (like a chest X-ray) is needed to check for active TB disease.
• Indeterminate: The test failed to produce a conclusive result and may need to be repeated.

When is the Test Used?

• Screening individuals at high risk of exposure.
• Evaluating patients who have had close contact with a known TB patient.
• As part of employment screenings (e.g., healthcare workers).