To the Editors:
We read with interest the study by van Leeuwen et al. 1 concerning the use of the T-SPOTTM.TB (Oxford Immunotec, Oxford, UK) interferon-γ release assay (IGRA) to rule out the diagnosis of active Mycobacterium tuberculosis infection. We disagree, however, with the use of the IGRA tests for ruling out active M. tuberculosis infection, especially in immunocompromised subjects. Sensitivity of T-SPOTTM.TB in immunocompromised subjects, although most certainly higher than that of tuberculin skin test (TST), is clearly <100%. The best sensitivities reported for HIV-infected subjects with active tuberculosis (TB) are 90% 2.
A Bayesian analysis of the cases presented illustrates the limitations of relying on IGRA tests to rule out TB 3, 4. In case A, a young female refugee from Bosnia develops a lingular infiltrate and has acid-fast bacilli (AFB) on examination of bronchoalveolar lavage (BAL). Incidence …