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Despite IGRA being specifically designed for latent TB there seems to be a growing need for IGRA to be used in active TB. I guess that given the nature of the active TB diagnostics it isn't quite so easy to diagnose active TB especially when the patient is unable to cough up enough material to diagnose, as is the case with children or the elderly or the sick.

In the UK they are now using IGRA to increase the sensitivity of the TST


Arch Dis Child. 2009 Nov 20. [Epub ahead of print]

Comparison of Interferon-gamma release assays and Tuberculin Skin Test in predicting active tuberculosis (TB) in children in the UK- a Paediatric TB Network Study.

Bamford AR, Crook AM, Clark J, Nademi Z, Dixon G, Paton JY, Riddell A, Drobniewski F, Riordan A, Anderson ST, Williams A, Walters S, Kampmann B.
Imperial College London, United Kingdom;

BACKGROUND: The value of interferon-gamma release assays (IGRA) to diagnose active tuberculosis (TB) in children is not established, but these assays are being widely used for this purpose. We examined the sensitivity of commercially available IGRA to diagnose active TB in children in the UK compared with the tuberculin skin test (TST).

METHODS: We established a paediatric tuberculosis network (PTBNET-UK) and conducted a retrospective analysis of data from children investigated for active TB at six large UK paediatric centres. All centres had used TST and at least one of the commercially available IGRA (T-Spot.TB or Quantiferon-Gold in Tube) in the diagnostic work up for active TB. Data were available from 333 children aged 2months to 16 years. We measured the sensitivity of TST and IGRA in definite (culture confirmed) and probable TB in children, agreement between TST and either IGRA and their combined sensitivity.

RESULTS: Of 333 children, 49 fulfilled the criteria of definite TB and 146 had probable TB. Within the definite cohort, TST had a sensitivity of 82%, Quantiferon-Gold in tube (QFT-IT) had a sensitivity of 78% and T-Spot.TB of 66%. Neither IGRA performed significantly better than a TST with a cut-off of 15 mm. Combining results of TST and IGRA increased the sensitivity to 96% for TST plus T-Spot.TB and 91% for TST plus QFG-IT in the definite TB cohort.

CONCLUSIONS: A negative IGRA does not exclude active TB disease, but a combination of TST and IGRA increases the sensitivity for identifying children with active TB.