A tuberculin skin test (TST; Mantoux) before BCG vaccination is only recommended in certain circumstances, based on risk factors for previous tuberculosis exposure
The need for TST should be determined by an individual risk assessment that considers whether the person:
- was born in a tuberculosis-endemic country (>40 cases per 100,000 population per year)
- has lived or travelled to a tuberculosis-endemic country or region (>40 cases per 100,000 population per year)
- had exposure to a close contact with tuberculosis or who is under investigation for tuberculosis
If an immunocompetent person who was required to have a TST is confirmed to be negative (induration of <5mm), they can receive BCG vaccine. A person with a TST of 5mm or greater or who has an accelerated BCG reaction (see below), should be considered for further investigation of latent or active tuberculosis.
The TST uses tuberculin, a purified protein derivative. This causes a hypersensitivity reaction in people who have previously been infected with Mycobacterium tuberculosis. ‘False positive’ hypersensitivity reactions can also occur in:
• people infected with other (non-tuberculous) mycobacteria
• people who have previously received BCG vaccine. Vaccination interferes with the interpretation of tuberculin skin test (TST) results
Interferon-gamma release assays (IGRAs) are a type of blood test that can detect M. tuberculosis infection (similar to the TST), but the TST is still the preferred method of screening for past tuberculosis exposure before BCG vaccination. Although TST and IGRA essentially provide the same information, there is uncertainty about whether hypersensitivity detected by IGRA is also associated with an accelerated local BCG reaction (as is the case with a positive TST).6
Both measles virus and measles-containing live attenuated vaccines 7,8 inhibit the response to tuberculin. TST-positive people may become TST-negative for 4–6 weeks after measles infection or vaccination. This should be taken into account when considering the timing of a TST in people who have had a measles-containing vaccine.
You can give a tuberculin skin test on the same day or visit with a COVID-19 vaccine. There is no specific time interval restriction between a tuberculin skin test and receiving a COVID-19 vaccine. Inhibition of response to a tuberculin skin test is not expected following administration of COVID-19 vaccines.
People with cellular immune compromise may also have a false negative TST, and BCG vaccination is generally contraindicated in this group since it is an attenuated live vaccine. See Contraindications and precautions.
Health professionals must correctly administer and interpret the TST. Consult state or territory tuberculosis guidelines for advice.