title: Discrepancy between the tuberculin skin test and the whole-blood interferon gamma assay for the diagnosis of latent tuberculosis infection in an intermediate tuberculosis-burden country.
abstract: BACKGROUND
  A recently developed whole-blood interferon gamma (IFN-gamma) assay based on stimulation with the Mycobacterium tuberculosis-specific antigens early secreted antigenic target 6 and culture filtrate protein 10 shows promise for the diagnosis of latent tuberculosis (TB) infection.
  
  
  OBJECTIVE
  To compare the tuberculin skin test (TST) and the whole-blood IFN-gamma assay in the diagnosis of latent TB infection according to the intensity of exposure.
  
  
  METHODS
  A prospective comparison between the whole-blood IFN-gamma assay and the TST using a 2-TU dose of purified protein derivative RT23 in a population with intermediate TB burden was conducted sequentially between February 1, 2004, and February 28, 2005, in a Korean tertiary referral hospital.
  
  
  METHODS
  Of 273 participants, 220 (95.7%) had received BCG vaccine. Participants were grouped according to their risk of infection: group 1, no identifiable risk of M tuberculosis infection (n = 99); group 2, recent casual contacts (n = 72); group 3, recent close contacts (n = 48); group 4, bacteriologically or pathologically confirmed TB patients (n = 54).
  
  
  METHODS
  Levels of agreement between the TST and the IFN-gamma assay and the likelihood of infection in the various groups.
  
  
  RESULTS
  For the TST with a 10-mm induration cutoff, the positive response rate in group 1 was 51%; group 2, 60%; group 3, 71%, and group 4, 78%. For the IFN-gamma assay, the positive response rate in group 1 was 4%; group 2, 10%; group 3, 44%; and group 4, 81%. The overall agreement between the TST and the IFN-gamma assay in healthy volunteers was kappa = 0.16. The odds of a positive test result per unit increase in exposure across the 4 groups increased by a factor of 5.31 (95% confidence interval [CI], 3.62-7.79) for the IFN-gamma assay and by a factor of 1.52 (95% CI, 1.20-1.91) for the TST (P<.001). Using a 15-mm induration cutoff for the TST did not make a substantial difference to the test results.
  
  
  CONCLUSIONS
  The IFN-gamma assay is a better indicator of the risk of M tuberculosis infection than TST in a BCG-vaccinated population.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine and Lung Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: Young Ae
authors.initials: YA
authors.lastname: Kang
authors.forename: Hye Won
authors.initials: HW
authors.lastname: Lee
authors.forename: Ho Il
authors.initials: HI
authors.lastname: Yoon
authors.forename: BeLong
authors.initials: B
authors.lastname: Cho
authors.forename: Sung Koo
authors.initials: SK
authors.lastname: Han
authors.forename: Young-Soo
authors.initials: YS
authors.lastname: Shim
authors.forename: Jae-Joon
authors.initials: JJ
authors.lastname: Yim
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000942:Antigens, Bacterial / Q000276:immunology; D001500:BCG Vaccine; D001426:Bacterial Proteins / Q000276:immunology; D005260:Female; D006801:Humans; D007371:Interferon-gamma / Q000276:immunology*; D007723:Korea; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000276:immunology / Q000302:isolation & purification* / Q000502:physiology; D012306:Risk; D014374:Tuberculin Test; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000276:immunology; D017735:Virus Latency
chemical_list: D000942:Antigens, Bacterial; D001500:BCG Vaccine; D001426:Bacterial Proteins; C117940:CFP-10 protein, Mycobacterium tuberculosis; C093276:ESAT-6 protein, Mycobacterium tuberculosis; D007371:Interferon-gamma