Sensitivity and specificity of a gamma interferon blood test for tuberculosis infection
OBJECTIVE: To determine the sensitivity and specificity of a gamma interferon (IFN-γ) blood test for tuberculosis infection.
Design: Heparinised blood samples from 952 volunteers were analysed using the QuantiFERON®-TB blood test. The levels of IFN-γ in whole blood aliquots stimulated in vitro with human, avian or bovine purified protein derivative (PPD), or phytohaemagglutinin (PHA), were compared to tuberculin reactivity and clinical presentation.
Results: IFN-γ (IU/ml) responses were expressed as % PPD/PHA response ratios. The proportion of responders detected by both the IFN-γ assay and tuberculin skin test (TST) was not significantly different when the % human PPD response ratio was 15%. Using this threshold, the specificity of the IFN-γ assay was 98% (407/417 individuals with no known exposure to tuberculosis were negative) and sensitivity was 90% (163/182 untreated TST reactors were positive). The test detected positive responses in 83% (10/12) of individuals with proven active disease, 59% (24/41) of those previously treated, 80% (134/168) of those with untreated inactive disease, and 43% (55/128) of those exposed but TST-negative.
Conclusion: The measurement of IFN-γ released from PPD-stimulated blood lymphocytes is a specific, sensitive and rapid method of detecting Mycobacterium tuberculosis infection. The IFN-γ assay may be a useful and practical tool for the early diagnosis of tuberculosis infection, especially in immunocompetent individuals.
Document Type: Regular Paper
Publication date: 1998-06-01
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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