Interferon Gamma Release Assay - TB

1. Quantiferon Gold
03.08.2018
Ahikam DJ

2. Rationale: Latent TB
• Incidence of TB: 14.4-43/100,000 in London
• 5% are <15 years
• 30% of those exposed get LTBI
• Of which 5-10% get disease
• In infants, risk of progression to pulmonary TB
is 30-40%; meningeal/miliary TB is 10-20%
• Treatment of LTBI reduces risk by 60% or more

3. https://www.google.co.in/url?sa=i&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwjr3N3a6s7cAhXGMo8KHfomD8YQjRx6BAgBEAU&url=https%3A%2F%2Fww
w.e7health.com%2Fcorporate-tb-skin-testing%2F&psig=AOvVaw2IdRMnsCqKcvoIAj2l56Lz&ust=1533314557033111

4. QFG: Mechanism
• In-vitro type 4 hypersensitivity reaction
• Antigens:
– ESAT-6: Early-secretory protein 6
– CFP-10: Culture-filtrate protein 10
– TB 7.7

5. QFG: Procedure
https://education.questdiagnostics.com/presentations/igras-in-the-diagnosis-of-tuberculosis?presentation_id=101

6. TST Vs IGRA
• In vivo
• 2- visit test
• Cheap
• In vitro
• BCG vaccination does
not produce false
positive

7. The Evidence
• Not much to prove superiority over TST in
specificity or sensitivity
• Glitch being non-availability of gold standard
to dectect LTBI
• Useful adjunct to evaluate children suspected
with TB
• Neither sensitive nor specific enought to rule
out or confirm TB

8. NICE Guidelines
• For those in close contact of TB
– Neonate
– <5 years
– >5 years
• Child from area of incidence greater than
40/100,000
• Child with immune suppression

9. Reference
• How to use: interferon γ release assay for
tuberculosis
Pollock et al. Arch Dis Child Educ Pract Ed 2013 98:99-105