Table 1

Comparison between TST and IGRA

TST (Mantoux test)IGRA
Basic test procedure ▸ Intradermal injection of tuberculin ▸ Area of induration around injection site is measured 48–72 h later ▸ ‘Cut-off’ measurements for positive test dependent on BCG status   ≥6 mm if no previous BCG   ≥15 mm if previous BCG Advantages ▸ Cheap ▸ Low tech (no lab required) Disadvantages ▸ Requires second visit to read result ▸ High interobserver and intraobserver variability in ‘reading’ result ▸ Reduced specificity in individuals with previous BCG or exposure to non-tuberculous mycobacteria ▸ Reduced sensitivity in young children and immune suppressionBasic test procedure ▸ Blood test requiring 3 ml (QFT-GIT) or 5 ml (T-SPOT.TB) of blood ▸ Test performed and reported by lab ▸ Can be done in 24 h, but labs may only run test 1–2 times per week Advantages ▸ Requires only one visit ▸ More objective result measurement ▸ More specific in individuals with prior BCG or previous exposure to most non-tuberculous mycobacteria Disadvantages ▸ More expensive ▸ Relatively high tech (requires laboratory facilities) ▸ Reduced sensitivity in young children and immune suppression
  • IGRA, interferon γ release assays; TST, tuberculin skin test.