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.
DESIGN: 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 (κ = 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).
CONCLUSION: 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.
Document Type: Regular Paper
Affiliations: 1: Escola Bahiana de Medicina e Saúde Pública, Salvador, Bahia, Brazil; and Hospital Especializado Octávio Mangabeira, Salvador, Bahia, Brazil 2: School of Public Health, University of California, Berkeley, California, USA 3: Escola Bahiana de Medicina e Saúde Pública, Salvador, Bahia, Brazil 4: Laboratório Integrado de Microbiologia e Imunorregulação, Salvador, Bahia, Brazil 5: Escola Bahiana de Medicina e Saúde Pública, Salvador, Bahia, Brazil; and Laboratório de Patologia e Biologia Molecular, Centro de Pesquisas Gonçalo Moniz, Salvador, Bahia, Brazil 6: Escola Bahiana de Medicina e Saúde Pública, Salvador, Bahia, Brazil; and Laboratório Avançado de Saúde Pública, Centro de Pesquisas Gonçalo Moniz, Salvador, Bahia, Brazil
Publication date: April 1, 2009
The International Journal of Tuberculosis and Lung Disease publishes articles on all aspects of lung health, including public health-related issues such as training programmes, cost-benefit analysis, legislation, epidemiology, intervention studies and health systems research. The IJTLD is dedicated to the continuing education of physicians and health personnel and the dissemination of information on tuberculosis and lung health world-wide.
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