Latent tuberculosis infection

Latent tuberculosis infection (LTBI)

Definition

• Prior exposure to TB
• Goal is to identify those who are at increased risk of developing active TB and would benefit from treatment

Investigations

• Tuberculin skin test (TBST)
  • Sens 90%, Spec >95
• Interferon-gamma release assay (IGRA)
  • Sn 95%, Sp >95%
  • Preferred for those who have received BCG after infancy

Positive TBST

1. Is it truly positive?
   • Consider IGRA
   • BCG vaccine can be considered a cause of false positive when
     • vaccine given after 12 months of age, and
     • patient has no risk factors, and
     • either Canadian-born non-Aboriginal, or not from endemic country
2. Rule out active TB
   • signs/symptoms
   • CXR or CT chest
   • Sputum x3 if coughing or cavitary lesions
3. Evaluate risk of reactivation treatment
   • INH 300 daily x9 mo with pyridoxine
   • baseline liver enzymes and vision testing

Reading

• TBST vs. IGRA for latent TB

Tools

• TST in 3D online TBST/IGRA Interpreter