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Free Content Role of whole-blood interferon-gamma release assay in the diagnosis of smear-negative tuberculosis

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SETTING: Hong Kong Chest Clinics.

OBJECTIVES AND METHODS: To conduct a prospective study investigating the role of a whole-blood interferon-gamma release assay, QuantiFERON®-TB Gold In-Tube (QFT-GIT), in the diagnosis of smear-negative tuberculosis (TB). The QFT-GIT result was compared with the final confirmed diagnosis after 12 months.

RESULTS: Of 262 smear-negative subjects, 188 had active TB, 167 (88.8%) of whom were QFT-GIT-positive; 74 had inactive/non-TB, 30 (40.5%) of whom were QFT-GIT-negative. The positive (PPV) and negative predictive values for active TB were respectively 79.1% and 58.8%. For this target group with high TB prevalence (71.8%), a positive test increased the chance of active disease by only 7.3%. Despite a positive likelihood ratio (LR) of 1.49, the negative LR was 0.28, making the diagnosis of active TB much less likely after a negative test. Although sensitivity and specificity showed no difference across different age groups, the PPV decreased (P < 0.001) with increasing age, likely reflecting the increased prevalence of competing diagnoses.

CONCLUSION: In an area with a high prevalence of latent TB infection, a positive QFT-GIT test does not add much to confirm the diagnosis of smear-negative TB, while a negative test indicates a need for further investigation.
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Keywords: Mycobacterium tuberculosis; active tuberculosis; interferon-gamma release assay

Document Type: Regular Paper

Affiliations: 1: Tuberculosis and Chest Service, Centre for Health Protection, Department of Health, Hong Kong, China 2: Tuberculosis Reference Laboratory, Public Health Laboratory Centre, Centre for Health Protection, Hong Kong, China 3: Tuberculosis and Chest Unit, Grantham Hospital, Hong Kong, Special Administrative Region, China

Publication date: 2010-12-01

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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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