Tuberculin Skin test (Mantoux test)

  • The prevalence of tuberculous infection may be estimated by the use of the tuberculin test in contradistinction to the clinical disease.
  • The positive test indicates that the individual has been infected by the tubercle bacillus sometime without necessarily showing overt signs or symptoms of disease.
  • A standardized tuberculin is available now through the World Health Organization.
  • It is available in the form of a purified protein derivative of Myco. tuberculosis (PPD/RT 23) with Tween 80 as a stabilizer.
  • It is the intra-cutaneous injection of the measured amount (usually 1 to 3 tuberculin units) which allows the comparison of the results obtained at different times and in different countries.
  • It is also known as Mantoux test.
  • A positive test appears as a delayed hypersensitivity tissue reaction, manifesting as an area of oedema (or induration) with a wider erythematous zone.
  • The diameter of the indurated area is measured after three days and the reading is expressed in millimeters.
  • In many warm climate countries where non-specific tuberculin reactions, presumably related to infection with mycobacteria other than mammalian tubercle bacilli, are common.
  • Only reactions of 10 or more mm are likely to indicate previous tuberculous infection.
  • The risk of misinterpreting tuberculin positive reactions in these communities may be minimized by dual tuberculin testing.
  • This is done with the PPD-S (or human) tuberculin plus tuberculin prepared from a non-mammalian species, e.g. PPD-B (or Battey).
  • Non-specific reactions are less common in most countries with temperate or colder climate where a positive test measuring 6 to 8mm is suggestive of tuberculous infection.

 

Heaf test

  • An alternative method of testing for hypersensitivity is done by a multiple puncture apparatus which pricks the skin through a film of stronger tuberculin.
  • This method is called Heaf test.
  • This method may also be used with undiluted BCG vaccine instead of tuberculin.
  • The Heaf test is read as grades 1 to 4 according to the degree of reaction.
  • While reading is done, grade 1 probably indicates a non-specific response.
  • This test has the advantage of speed, acceptability and reproducibility but is not so easily standardized as the Mantoux test.

 

Image result for heaf test                                  Image result for tuberculin test

 

Application and uses of tuberculin test

  • Tuberculin tests to measure the prevalence of infection may be applied to the children at school entry (5 to 6 years) or at 10 to 13 years.
  • In Britain it is used as the preliminary screening test before BCG vaccination.
  • This test is used in contact tracing of infectious cases of tuberculosis in the families and close relatives of young children who give positive reactions.
  • It is also used as an aid to the clinical diagnosis of suspected infection in young children.
  • It is also used as an indication of early clinical infection in older children who give strongly positive reactions (15mm or more). These kinds of children require regular follow up with X-ray examinations for 2 to 3 years.
  • It is also used as a post-vaccination check on the efficacy of BCG vaccination.

References: 

i) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3481914/

ii) https://www.healthywa.wa.gov.au/Articles/S_T/Tuberculin-Skin-Test

Tuberculin Skin test (Mantoux test)