Comparison of a whole-blood interferon-γ assay and tuberculin skin testing in patients with active tuberculosis and individuals at high or low risk of Mycobacterium tuberculosis infection

Background: QuantiFeron-TB (QIFN) is a whole-blood interferon-γ assay for the recognition of cell-mediated immune response to Mycobacterium tuberculosis infection. Objectives: To compare the QIFN assay with the tuberculin skin test (TST) in patients with newly diagnosed culture-proven tuberculosis (TB) and healthy volunteers with high or low risk of latent M tuberculosis infection and to identify factors associated with discordance between tests. Method: Two-hundred fifty-eight subjects underwent both assays. All participants completed a detailed questionnaire, and data from TB patients' medical records were collected. Results: In the entire study population, agreement between tests was moderate and the correlation between the magnitude of QIFN response and the TST induration diameter was significant. In volunteers with no known risk of exposure to M tuberculosis, the specificity of the assays was comparable. However, in subjects with active TB or those vaccinated with bacille Calmette...