title: Predictors for a positive QuantiFERON-TB-Gold test in BCG-vaccinated adults with a positive tuberculin skin test.
abstract: BACKGROUND
  Prevention of tuberculosis (TB) in the United States usually involves testing for latent tuberculosis infection (LTBI) with a tuberculin skin test (TST), followed by offering therapy to those who have a positive test result. QuantiFERON-TB Gold assay (QFT-G) is more specific for infection with Mycobacterium tuberculosis than the TST, especially among persons vaccinated with bacillus Calmette-Guérin, thereby reducing the number of false positive tests.
  
  
  METHODS
  Adults referred to a pulmonary clinic for a positive TST result were tested with QFT-G. We assessed factors for having a positive QFT-G.
  
  
  RESULTS
  Among 100 adults who were BCG-vaccinated and had a positive TST result, 30 (30%) had a positive result using QFT-G. Persons from high-incidence countries were 8.2 times more likely to have a positive QFT-G result compared with persons from low-incidence countries (46% versus 9%). Using logistic regression to assess QFT-G positivity, strong predictors included having an abnormal chest radiograph consistent with healed TB, a TST induration of ≥16mm, and birth in a high-incidence country.
  
  
  CONCLUSIONS
  Use of QFT-G assay following a positive TST result further identifies persons who would most benefit from treatment for LTBI.
authors.affiliation: Department of Medicine, University of Connecticut Medical Center, Farmington, CT, USA.
authors.forename: Harsh
authors.initials: H
authors.lastname: Chawla
authors.forename: Mark N
authors.initials: MN
authors.lastname: Lobato
authors.forename: Lynn E
authors.initials: LE
authors.lastname: Sosa
authors.forename: Richard
authors.initials: R
authors.lastname: ZuWallack
mesh_terms: D000328:Adult; D001500:BCG Vaccine / Q000008:administration & dosage*; D015331:Cohort Studies; D003955:Diagnostic Tests, Routine / Q000379:methods*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D015994:Incidence; D055985:Latent Tuberculosis / Q000175:diagnosis* / Q000382:microbiology; D016015:Logistic Models; D008297:Male; D009169:Mycobacterium tuberculosis; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D014374:Tuberculin Test; D014376:Tuberculosis / Q000175:diagnosis / Q000382:microbiology / Q000517:prevention & control*
chemical_list: D001500:BCG Vaccine