Mycobacterium Tuberculosis Antigen-Specific Interferon-Gamma Release Assay

1. See Also
   1. Tuberculosis
   2. Tuberculin Skin Test
2. Indications
   1. Mycobacterium tuberculosis testing
   2. May be indicated in health care settings, homeless shelters and prisons for suspected contacts
   3. Consider as pre-screening before starting immune suppressants or immune modulators (e.g. TNF agents)
   4. Consider for positive PPD in immigrants to differentiate BCG versus latent Tuberculosis
3. Contraindications
   1. Children under age 5 years
4. Mechanism
   1. Lab assay specific for prior Mycobacterium tuberculosis exposure
   2. Detects interferon-gamma release
      1. Originates from memory T-cells
      2. Released by cells previously sensitized to Mycobacterium tuberculosis-specific proteins
5. Efficacy
   1. Does not distinguish latent from active Tuberculosis
   2. False negatives occur in immunocompromised patients
   3. No false positives with prior BCG vaccination
   4. No false positives with non-TuberculosisMycobacterium strains
6. Disadvantages
   1. Sample must be tested within 12 hours of being obtained
   2. Old test was more labor intensive and expensive
      1. Newer tests (QFT-GIT, T-Spot) are more easily run now
   3. QFT-GIT is effected by immune status
      1. T-Spot is not limited by immune status