Clinical inquiries. How should we manage a patient with a positive PPD and prior BCG vaccination?

Prior bacille Calmette-Guerin (BCG) vaccination increases the likelihood of a positive tuberculosis (TB) 5TU purified protein derivative (PPD) skin test. The PPD response following BCG vaccine varies with age at vaccination, number of years since the BCG vaccination, number of times vaccinated, and number of PPDs performed. An induration of greater than 14 mm is unlikely to be due to prior BCG vaccination (strength of recommendation [SOR]: A, based on meta-analysis of validation cohort studies). The variable reaction after BCG vaccination, along with the desire to detect all cases of TB, has led to recommendations that all patients with a positive PPD test be treated as true positives. These patients should undergo chest radiography and appropriate treatment, regardless of history of BCG vaccine (SOR: B, extrapolation from level 1 study). A recently developed alternative is the interferon-gamma assay (QuantiFERON-TB Gold test), which may be used in place of, or in addition to, the PPD skin test for patients who are known to have received a BCG vaccine (SOR: B, extrapolation from a validation cohort study).