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

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
Rule out active TB
- signs/symptoms
- CXR or CT chest
- Sputum x3 if coughing or cavitary lesions
Evaluate risk of reactivation treatment
- INH 300 daily x9 mo with pyridoxine
- baseline liver enzymes and vision testing