Use of tuberculin skin test, chest radiograph and interferon-gamma release assay to select migrants for treatment of latent tuberculosis

Australian guidelines recommend the tuberculin skin test (TST) as the preferred test for latent tuberculosis infection (LTBI) with interferon-gamma release assay (IGRA) as a supplemental test to improve specificity. For many years the chest radiograph has been used to interpret a TST in the 5-9 mm range. The chest radiograph is known to predict subsequent reactivation of tuberculosis (TB). We report a retrospective database review of the Migrant Screening Clinic at Western Health Footscray Hospital during the period April 2010 to November 2011. Of 129 migrants under 35 years of age with TST 5-14 mm, IGRA was positive in 37 (28.7%). IGRA was positive in 7.7% of those with TST 5-9 mm and chest radiograph not suggestive of TB disease, 28.6% in those with TST 5-9 mm and chest radiograph that was suggestive of TB disease, and 39.5% in those with TST 10-14 mm (? 2 trend=12.5, p=0.0004). There were 21 (16%) of 129 persons who had a negative IGRA but both TST >= 5 mm and a chest radiograph suggestive of TB disease. These data support existing recommendations to use the chest radiograph when interpreting a TST of 5-9 mm and recommending treatment of LTBI.