Tuberculin test

In the UK, this test is offered to those at risk of tuberculosis (TB) (e.g. health workers, TB contacts) and those 10-13 years, to find those needing BCG vaccination.

In the Mantoux test purified protein derivative (tuberculin) is injected intradermally and the result is read two to three days later.

• the greater the reaction, the more likely it is that an individual is infected or has active TB disease

Interpretation of result (1):

• Mantoux negative - Induration less than 6 mm
• Mantoux positive - Induration 6 mm or greater
• Mantoux strongly positive- Induration 15 mm or greater

A positive result implies previous exposure to tuberculin protein - thus it could represent previous BCG exposure.

It is a type IV hypersensitivity reaction.

Alternative tuberculin tests are available for large-scale screening (Heaf and Tine tests) but they are not as accurate as the Mantoux test.

• it has been recommended that the Mantoux test should be standard method of tuberculin testing (1)

Notes:

• NICE have issued guidance concerning the diagnosis of latent TB in adults (2):
  • offer Mantoux testing to diagnose latent TB in adults aged 18 to 65 who are close contacts of a person with pulmonary or laryngeal TB
    • if the Mantoux test is inconclusive, refer the person to a TB specialist
    • if the Mantoux test is positive (an induration of 5 mm or larger, regardless of BCG history) assess for active TB
    • if the Mantoux test is positive but a diagnosis of active TB is excluded, consider an interferon gamma release assay if more evidence of infection is needed to decide on treatment. This could be, for example, if the person needs enhanced case management or if there could be adverse events from treatment
    • if the Mantoux is positive, and if an IGRA was done and that is also positive, offer them treatment for latent TB infection
      
      
• BCG should not be administered to an individual with a positive tuberculin test (3)
  • it is unnecessary and may cause a more severe local reaction
  • a tuberculin skin test is necessary prior to BCG vaccination for:
    • all individuals aged six years or over
    • infants and children under six years of age with a history of residence or prolonged stay (more than three months) in a country with an annual TB incidence of 40/100,000 or greater
    • those who have had close contact with a person with known TB
    • those who have a family history of TB within the last five years
  • BCG can be given up to three months following a negative tuberculin test
    
    
• Factors affecting the result of the tuberculin test (3)
  • reaction to tuberculin protein may be suppressed by the following:
    • glandular fever
    • viral infections such as measles and varicella zoster (chickenpox) but NOT upper respiratory tract infections or gastroenteritis
    • live viral vaccines (tuberculin testing should not be carried out within four weeks of having received an injectable live viral vaccine)
    • sarcoidosis
    • corticosteroid therapy
    • immunosuppression due to disease or treatment, including HIV infection
  • subjects who have a negative test but who may have had a significant infection (such as measles, varicella zoster (chickenpox), scarlet fever, glandular fever) at the time of testing or at the time of reading should be re-tested two to three weeks after clinical recovery before being given BCG. If a second tuberculin test is necessary it should be carried out on the other arm: repeat testing at one site may alter the reactivity either by hypo- or more often hyper-sensitising the skin, and a changed response may reflect local changes in skin sensitivity only

Reference:

1. Department of Health (July 6th 2005). Changes to the BCG Vaccination Programme. PL/CMO/2005/3, PL/CNO/2005/3, PL/CPHO/2005/3.
2. NICE (May 2016). Tuberculosis Clinical diagnosis and management of tuberculosis, and measures for its prevention and control
3. The Green Book. Chapter 19 - Tuberculosis (April 2019)