title: Analysis of discordance between the tuberculin skin test and the interferon-gamma release assay.
abstract: OBJECTIVE
  To analyze factors associated with discordance between tuberculin skin test (TST) and interferon-gamma release assay (IGRA) results among household contacts of pulmonary tuberculosis (PTB) patients.
  
  
  METHODS
  TST (purified protein derivative) and IGRA (QuantiFERON-TB Gold) were performed on household contacts of PTB patients diagnosed between 2006 and 2007 in Salvador, Brazil. Discordant test groups were compared with the TST-/IGRA- group.
  
  
  RESULTS
  Of 261 household contacts satisfactorily tested by TST, 145 (55.6%) had positive TST results; of 298 satisfactorily tested by IGRA, 127 (43.1%) had positive results. The test agreement was 0.76 (kappa = 0.53, 95%CI 0.43-0.63). Sixty-one (24%) were discordant: 44 (72%) with TST+/IGRA- and 17 (28%) with TST-/IGRA+ results. Compared to the TST-/IGRA- group, the TST+/IGRA- and TST+/IGRA+ groups were significantly more likely to have a chest X-ray showing old lung scars (OR = 6.8, 95%CI 1.3-35.0; OR = 7.4, 95%CI 2.2-24.4, respectively). The TST-/IGRA+ group was exposed to their index cases for significantly longer than the TST-/IGRA- group (OR = 7.2, 95%CI 1.7-29.3).
  
  
  CONCLUSIONS
  The TST+/IGRA- and TST+/IGRA+ groups shared more similar characteristics with each other than with the TST-/IGRA- group. In a setting endemic for TB, TST results appear to be more suitable in the decision to treat latent TB infection.
authors.affiliation: Escola Bahiana de Medicina e Saúde Pública, Salvador, Bahia, Brazil; Hospital Especializado Octávio Mangabeira, Salvador, Bahia, Brazil. almeriojr@yahoo.com.br
authors.forename: A
authors.initials: A
authors.lastname: Machado
authors.forename: K
authors.initials: K
authors.lastname: Emodi
authors.forename: I
authors.initials: I
authors.lastname: Takenami
authors.forename: B C
authors.initials: BC
authors.lastname: Finkmoore
authors.forename: T
authors.initials: T
authors.lastname: Barbosa
authors.forename: J
authors.initials: J
authors.lastname: Carvalho
authors.forename: L
authors.initials: L
authors.lastname: Cavalcanti
authors.forename: G
authors.initials: G
authors.lastname: Santos
authors.forename: M
authors.initials: M
authors.lastname: Tavares
authors.forename: M
authors.initials: M
authors.lastname: Mota
authors.forename: F
authors.initials: F
authors.lastname: Barreto
authors.forename: M G
authors.initials: MG
authors.lastname: Reis
authors.forename: S
authors.initials: S
authors.lastname: Arruda
authors.forename: L W
authors.initials: LW
authors.lastname: Riley