Table 13.18-5. Tuberculin skin test cut-points for treatment of latent tuberculosis infection

TST result

Indication1

0-4 mm

– In general, this is considered negative and no treatment is indicated2

– Close contacts in children <5 years of age should be treated pending results of repeat skin test 8 weeks after exposure3

≥5 mm

– HIV infection

– Contact with infectious TB within the past 2 years

– Fibronodular disease on chest radiographs (healed TB and not previously treated)

– Organ transplantation (related to immune suppressant therapy)4

– Tumor necrosis factor alpha inhibitors

– Other immunosuppressive drugs, eg, glucocorticoids (equivalent of ≥15 mg/d of prednisone for 1 month or more; risk of TB disease increases with higher dose and longer duration)

– End-stage renal disease

≥10 mm

All others, including the following specific situations:

– TST conversion (within 2 years)

– Diabetes, malnutrition (<90% ideal body weight), cigarette smoking, daily alcohol consumption (>3 drinks/d)

– Silicosis

– Hematologic malignancies (leukemia, lymphoma) and certain carcinomas (eg, head and neck)

1 Age ≥35 years is not a contraindication to treatment of LTBI if the risk of progression to active TB disease is greater than the risk of serious adverse reactions to treatment.

2 Treatment with isoniazid of people with HIV infection who were TST negative (0-4 mm) and/or anergic was of no benefit in several randomized trials. Other authorities suggest this treatment may be considered in the presence of HIV infection or other cause of severe immunosuppression and high risk of TB infection (contact with infectious TB, from high TB-incidence country or abnormal chest radiographs consistent with prior TB infection). Hence any decision to give treatment should be individualized in consultation with a TB expert.

3 If first TST is negative, begin treatment immediately. Repeat TST 8 weeks after exposure to infectious TB case ended. Treatment can be stopped in a healthy child if repeat TST is negative (<5 mm induration). In children <6 months of age, the immune system may not be mature enough to produce a positive TST, even if the child is infected.

4 LTBI therapy is often given to people in whom transplantation is planned but before the actual transplantation.

Source: ©All Rights Reserved. Canadian Tuberculosis Standards, 7th Edition. The Public Health Agency of Canada, The Lung Association, and the Canadian Thoracic Society, 2014. Adapted and reproduced with permission from the Minister of Health, 2016.

HIV, human immunodeficiency virus; LTBI, latent tuberculosis infection; TB, tuberculosis; TST, tuberculin skin test.