What is a TST?

The TST is done to identify individuals with latent Tuberculosis (TB) infection (LTBI) who are at risk of developing TB disease. A TST is not used to diagnose TB disease. Identification and treatment of LTBI can substantially reduce the risk of developing TB disease. This protects the health of the individual as well as the public.

When is a TST recommended?

Individuals with increased risk of TB exposure, and for whom treatment of LTBI would be considered are recommended to receive a TST. TST is commonly recommended for:

• Contacts of an individual diagnosed with pulmonary TB
• Individuals born in TB endemic countries
• Individuals with health conditions such as HIV, diabetes, and chronic renal failure that would increase the risk of developing TB
• Individuals who are homeless or underhoused
• Individuals who use injection drugs
• Indigenous people from areas with high TB incidence
• Health care workers
• Residents of correctional facilities, retirement homes and long-term care homes (< 65 years of age)
• Travelers to areas of high TB incidence 

When is a TST not recommended?

The TST is not recommended for anyone who:

• Had a previous positive TST result, or had a severe blistering reaction
• Had previous anaphylaxis or hypersensitivity reaction
• Has been diagnosed with or treated for TB in the past
• Has extensive burns or eczema
• Has a current major viral infection, or has received a live virus immunization within the past 4 weeks
• Is a resident of long-term care home or retirement home >65 years of age

The following do not prevent you from getting a TST:

• Receiving Bcg vaccine in the past
• Common cold or mild viral illness
• Pregnancy or breastfeeding
• Immunization with vaccine on the same day
• A previous positive TST reaction that was not documented

What is a two-step TST?

A two-step TST is used to establish a baseline for people who will be tested regularly.

To perform the two-step TST, a healthcare professional will administer and read the first TST. If the result is negative, they will repeat a second TST one to four weeks later (no sooner than one week and no later than four weeks). The result of the second TST is the true baseline.

A two-step TST needs to be performed only once if properly administered and documented. Any TST afterwards can be one-step, regardless of how long it has been since the last TST.

Additional Information

• RCDHU: Positive Mantoux Skit Test Report
• RCDHU: Contact
• Canadian Tuberculosis Standards: Chapter 4-Diagnosis of tuberculosis infection