Screening for latent TB

• Whom to screen:
  • high likelihood of exposure and/or high risk of progression to active disease
  • including HIV ⊕ and prior to immunosuppression (pre-transplant or anti-TNF)
• Relies on host immune system, so limited Se in immunosuppressed individuals
• NB: testing for host exposure & immune response to TB, not whether TB active (vide infra)
• Screening tests:
  • IFN-γ release assays (IGRA):
    • preferred test;
    • Ag-stimulated IFN-γ release from Pt’s T-cells.
    • ↑ Sp over TST/PPD in BCG vaccinated Pts.
  • Tuberculin skin test