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J Infect Public Health. 2012 Dec;5(6):369-73. doi: 10.1016/j.jiph.2012.06.003. Epub 2012 Oct 27.

Predictors for a positive QuantiFERON-TB-Gold test in BCG-vaccinated adults with a positive tuberculin skin test.

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Department of Medicine, University of Connecticut Medical Center, Farmington, CT, USA.



Prevention of tuberculosis (TB) in the United States usually involves testing for latent tuberculosis infection (LTBI) with a tuberculin skin test (TST), followed by offering therapy to those who have a positive test result. QuantiFERON-TB Gold assay (QFT-G) is more specific for infection with Mycobacterium tuberculosis than the TST, especially among persons vaccinated with bacillus Calmette-Guérin, thereby reducing the number of false positive tests.


Adults referred to a pulmonary clinic for a positive TST result were tested with QFT-G. We assessed factors for having a positive QFT-G.


Among 100 adults who were BCG-vaccinated and had a positive TST result, 30 (30%) had a positive result using QFT-G. Persons from high-incidence countries were 8.2 times more likely to have a positive QFT-G result compared with persons from low-incidence countries (46% versus 9%). Using logistic regression to assess QFT-G positivity, strong predictors included having an abnormal chest radiograph consistent with healed TB, a TST induration of ≥16mm, and birth in a high-incidence country.


Use of QFT-G assay following a positive TST result further identifies persons who would most benefit from treatment for LTBI.

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