• Tuberculosis

Screening for latent infection with Mycobacterium tuberculosis (LTBI) and treatment of test-positives is the cornerstone in the prevention of TB and should be performed preferably among individuals with risk for progression. Progression from LTBI to active TB is highest in recent contacts of patients with active TB. Moreover, it is considered particularly high in latently infected patients if they are also immunodeficient. Therefore, screening for evidence of LTBI is recommended for HIV-infected individuals, patients with chronic renal failure, individuals receiving immunosuppressive drug therapy following solid organ or stem cell transplantation, and patients with autoimmune diseases.1 ,2 Since by definition LTBI lacks the gold standard of bacteriological confirmation, the condition is diagnosed indirectly by detection of an immune response towards mycobacterial antigens with either the tuberculin skin test (TST) or interferon-γ release assays (IGRA) performed from whole blood. IGRA may have test-intrinsic and operational advantages over the TST: due to the use of M. tuberculosis-specific antigens, IGRA have been shown to be more specific than the TST and allow distinction of infections with M. tuberculosis from immunity towards bacille Calmette–Guérin (BCG) or most non-tuberculous mycobacteria.3 Moreover, unlike the TST, which has been shown to be of low sensitivity in immunocompromised patients, IGRA seem to be less affected by immunodeficiency, as frequently reflected by a higher percentage of positive test results in IGRA compared with TST in head-to-head comparative analyses.4 Finally, as IGRA are performed along with negative and positive controls, indeterminate results due to failure of responses in the positive control (phytohaemagglutinin) may increase with increasing immunodeficiency and potentially allow to discriminate true negative from falsely negative test results. Our knowledge about the effect of immunosuppressive drugs on TST and IGRA results remains somewhat limited as the individual studies published to date suffer from sample sizes, …