title: In routine UK hospital practice T-SPOT.TB™ is useful in some patients with a modest pre-test probability of active tuberculosis.
abstract: OBJECTIVE
  to assess the usefulness of the T-SPOT.TB™ interferon-gamma release assay (IGRA), as used in a regional hospital infectious diseases unit in Northwest England, for the diagnosis of active tuberculosis.
  
  
  METHODS
  Retrospective case series.
  
  
  RESULTS
  T-SPOT.TB™ test was applied to a group of 64 patients, 20 of whom had tuberculosis (mostly extra-pulmonary tuberculosis). The T-SPOT.TB™ test had a sensitivity of 83.3% and a specificity of 75% for the diagnosis of active tuberculosis, compared with culture. A positive IGRA approximately doubled the pre-test probability of disease from 0.23 to 0.5. This doubling of probability was true regardless of HIV status, though for HIV+ patients the sensitivity was lower (sensitivity 66.7%, post test probability 0.4 for a positive IGRA result). When extrapolated to the local population the test was most useful for exclusion of disease; post test probability 0.006 (or 1 in 167) for a negative IGRA result.
  
  
  CONCLUSIONS
  Although it can add weight to a clinical diagnosis, T-SPOT.TB™ assay is not reliable for the diagnosis of active tuberculosis in a real world setting where the test is often used in patients with smear negative or extra-pulmonary disease. The test is useful for ruling out disease in HIV negative patients.
authors.affiliation: Tropical and Infectious Disease Unit, Royal Liverpool University Hospital, Prescot Street, Liverpool L7 8XP, UK.
authors.forename: Lance
authors.initials: L
authors.lastname: Turtle
authors.forename: Tim
authors.initials: T
authors.lastname: Kemp
authors.forename: Geraint R
authors.initials: GR
authors.lastname: Davies
authors.forename: S Bertie
authors.initials: SB
authors.lastname: Squire
authors.forename: Nick J
authors.initials: NJ
authors.lastname: Beeching
authors.forename: Michael B J
authors.initials: MB
authors.lastname: Beadsworth
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D059425:Interferon-gamma Release Tests; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000276:immunology; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014376:Tuberculosis / Q000175:diagnosis*; D006113:United Kingdom; D055815:Young Adult