title: Interferon gamma release assays for diagnosing active and latent tuberculosis.
abstract: BACKGROUND
  In view of the continuing global epidemic of tuberculosis (TB), adequate diagnosis is crucial for controlling this disease. Two commercial interferon gamma release assays (IGRA) have become available: the QuantiFERON-TB (QFT) and the T-SPOT.TB (TSPOT). They offer an important new tool for detecting both latent and active TB. In particular, the increased specificity as compared with the tuberculin skin test (TST) has resulted in many now (considering) replacing TST with IGRA.
  
  
  OBJECTIVE
  This review tries to offer the reader more insight from a clinical perspective into the applicability of IGRA for both latent and active TB.
  
  
  CONCLUSIONS
  Although both IGRA are based on the same principle, they have marked different performance characteristics and it seems likely that both assays will establish their own niche. The increased specificity and sensitivity of IGRA in various settings as compared with TST show us that IGRA are here to stay. QFT might be the preferred tool for large-scale contact tracing, but in most clinical settings TSPOT has to be preferred. Much knowledge on IGRA has already been obtained in a short time; however, many questions remain unresolved, such as likelihood for developing active TB in individuals with a negative IGRA in contact tracing in various subgroups and the applicability of IGRA for detecting active TB.
authors.affiliation: Medical Microbiologist, Department of Medical Microbiology, Diakonessenhuis, Bosboomstraat 1, 3582 KE Utrecht, The Netherlands sthijsen@diakhuis.nl.
authors.forename: Steven Ft
authors.initials: SF
authors.lastname: Thijsen
authors.forename: Ailko Wj
authors.initials: AW
authors.lastname: Bossink