The Mantoux tuberculin skin test (TST) is the standard method of determining whether a person is infected with Mycobacterium tuberculosis. Reliable administration and reading of the TST requires standardization of procedures, training, supervision, and practice. The diagnosis of tuberculosis in children by demonstration of the bacilli is difficult as the disease is usually paucibacillary. Hence indirect evidence of tests like the Tuberculin test becomes all the more important.
Tuberculin has come a long way from Kochâ€™s Old Tuberculin (OT) in the 1890s to the current PPDs in use. The Purified Protein Derivative (PPD) was initially derived by TCA precipitation of culture filtrates by Florence Siebert in 1941. That was accepted by the WHO as the standard preparation PPD-S (PPD-Standard). Another preparation of PPD was made by Siebert at the Statens Serum Institute, Copenhagen in 1958, the PPD-RT23. This was accepted as the international standard. Later a detergent, Tween 80 was added to the PPD to prevent its adsorption to glass vials & syringes. Hence, currently, there are only two standard preparations of PPD: PPD-S and PPD RT23. 1 tuberculin unit (TU) of PPD RT23 is equivalent to 2.5 TU of PPD-S. In India as PPD RT 23 is available, 2 TU of PPD RT23 should be used, as an equivalent to 5 TU of PPD-S, as per international recommendations.
The usefulness of the test lies not only on proper technique of administering a standard dose of a standard tuberculin and reading of the reactions by trained personnel but also in its careful interpretation.
There are three types of Tuberculin Skin Tests (TST): the multiple puncture,
or Heaf test; the Tine test and the intradermal Mantoux test. The Heaf
and the Tine test have poor specificity and sensitivity, and are better
avoided. For all practical purposes, the intradermal tuberculin skin test is
the internationally accepted standard TST for diagnostic and
epidemiological purposes. PPD is available in multi-dose vials of 10 or 50 tests that must be refrigerated at 2 â€“ 8 deg C and discarded within 1 month of opening the vial.