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Free Content Accuracy of an interferon-γ release assay to detect active pulmonary and extra-pulmonary tuberculosis

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OBJECTIVE: To examine the performance of an interferon-gamma (IFN-γ) release assay (QuantiFERON-TB 2G assay [QFT-G]) to detect Mycobacterium tuberculosis infection in a Japanese general hospital, for the diagnosis of active pulmonary tuberculosis (PTB) and extra-pulmonary tuberculosis (EPTB).

DESIGN: We prospectively examined the performance of QFT-G in 194 patients suspected of active TB. Diagnosis was confirmed by 1) positive M. tuberculosis cultures, or 2) clinical manifestations or laboratory or pathological findings consistent with active TB and response to specific therapy.

RESULTS: Three patients with indeterminate QFT-G results were excluded. Among the remaining 191 patients, 77 had active TB. When the cut-off concentration of IFN-γ was set at 0.35 IU/ml, as recommended by the manufacturer, the assay was positive in 69 patients and negative in 122. The sensitivity of the assay was 76.6% in all patients, 74.5% in the 47 patients with PTB and 80.0% in the 30 patients with EPTB. The overall specificity of the assay was 91.2%.

CONCLUSION: Although the specificity of the QFT-G to detect active TB was high and its sensitivity low, it was as accurate for the detection of active EPTB as for PTB when the 0.35 IU/ml INF-γ cut-off concentration was used.
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Keywords: Mycobacterium tuberculosis; extra-pulmonary tuberculosis; interferon-gamma

Document Type: Regular Paper

Affiliations: 1: Division of Pulmonary Medicine, Department of Medicine, Keio University School of Medicine, Tokyo, Japan 2: Health Center, Keio University, Kanagawa, Japan 3: Department of Preventive Medicine and Public Health, Keio University School of Medicine, Tokyo, Japan 4: Immunology Division, Research Institute of Tuberculosis, Japanese Anti-Tuberculosis Association, Tokyo, Japan

Publication date: 01 March 2008

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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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