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