title: Sensitivity and specificity of a gamma interferon blood test for tuberculosis infection.
abstract: METHODS
  Victoria, Australia.
  
  
  OBJECTIVE
  To determine the sensitivity and specificity of a gamma interferon (IFN-gamma) blood test for tuberculosis infection.
  
  
  METHODS
  Heparinised blood samples from 952 volunteers were analysed using the QuantiFERON-TB blood test. The levels of IFN-gamma in whole blood aliquots stimulated in vitro with human, avian or bovine purified protein derivative (PPD), or phytohaemagglutinin (PHA), were compared to tuberculin reactivity and clinical presentation.
  
  
  RESULTS
  IFN-gamma (IU/ml) responses were expressed as % PPD/PHA response ratios. The proportion of responders detected by both the IFN-gamma assay and tuberculin skin test (TST) was not significantly different when the % human PPD response ratio was 15%. Using this threshold, the specificity of the IFN-gamma assay was 98% (407/417 individuals with no known exposure to tuberculosis were negative) and sensitivity was 90% (163/182 untreated TST reactors were positive). The test detected positive responses in 83% (10/12) of individuals with proven active disease, 59% (24/41) of those previously treated, 80% (134/168) of those with untreated inactive disease, and 43% (55/128) of those exposed but TST-negative.
  
  
  CONCLUSIONS
  The measurement of IFN-gamma released from PPD-stimulated blood lymphocytes is a specific, sensitive and rapid method of detecting Mycobacterium tuberculosis infection. The IFN-gamma assay may be a useful and practical tool for the early diagnosis of tuberculosis infection, especially in immunocompetent individuals.
authors.affiliation: Mercy Private Hospital Consulting Suites, East Melbourne, VIC, Australia.
authors.forename: J A
authors.initials: JA
authors.lastname: Streeton
authors.forename: N
authors.initials: N
authors.lastname: Desem
authors.forename: S L
authors.initials: SL
authors.lastname: Jones
mesh_terms: D000328:Adult; D000818:Animals; D002417:Cattle; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007371:Interferon-gamma / Q000097:blood*; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000276:immunology; D008297:Male; D008875:Middle Aged; D009162:Mycobacterium avium; D009163:Mycobacterium bovis; D012372:ROC Curve; D012680:Sensitivity and Specificity; D014373:Tuberculin / Q000494:pharmacology; D014374:Tuberculin Test; D014376:Tuberculosis / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology
chemical_list: D014373:Tuberculin; D007371:Interferon-gamma