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Free Content Intra-assay reliability and robustness of QuantiFERON®-TB Gold In-Tube test in Zambia

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Abstract:

BACKGROUND: Interferon-gamma (IFN-γ) release assays (IGRAs), such as the QuantiFERON®-TB Gold In-Tube test (QFT-GIT), are becoming a preferred method for diagnosis of tuberculosis (TB) infection in many industrialised countries. However, data on the effectiveness of IGRAs in high TB-HIV (human immunodeficiency virus) endemic and resource-limited settings, such as Zambia, are limited.

OBJECTIVE: To determine the intra-assay reliability and robustness of QFT-GIT in a field setting in Zambia.

DESIGN: During July–October 2007, 109 adult smear-positive TB patients were recruited to determine QFT-GIT reliability and the effect of a 24-h delay in incubation. Two simulated laboratory experiments were also performed using 9–14 volunteers, to explore the effect of power outages during incubation and storage temperature of collection tubes on IFN-γ responses.

RESULTS: QFT-GIT intra-assay concordance was 91.7% (κ = 0.8). Discordance was observed for nine patients, of whom six were HIV-positive. There was evidence of an association between HIV status and discordant results (OR 1.98, 95%CI 1.06–3.67, P = 0.03). A 24-h delay in incubation changed results for 25 of the 109 (22.9%) patients. Power outages that altered incubation time reduced IFN-γ responses.

CONCLUSION: Although QFT-GIT seems reliable in this setting, we have identified operational factors that affect its robustness. These factors may influence the effectiveness of this test in similar resource-limited settings.

Keywords: HIV; QuantiFERON-TB Gold In-Tube; Zambia; reliability; tuberculosis

Document Type: Regular Paper

Affiliations: 1: Zambia AIDS-Related Tuberculosis (ZAMBART) Project, University of Zambia, Lusaka, Zambia 2: Zambia AIDS-Related Tuberculosis (ZAMBART) Project, University of Zambia, Lusaka, Zambia; and London School of Hygiene & Tropical Medicine, London, UK 3: London School of Hygiene & Tropical Medicine, London, UK

Publication date: 2010-07-01

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  • 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.

    Certain IJTLD articles are selected for translation into French, Spanish, Chinese or Russian. They are available on the Union website

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