A discrete, pale elevation of the skin (a wheal) 6 to 10 mm in diameter should be produced when the injection is given correctly. It is to be injected strictly intradermally, using 28 or 26-gauge needle and tuberculin syringe from which 0.1 ml can be delivered accurately. For the sake of standardization of reading and interpretation of results, 5 TU of tuberculin PPD RT23 is used almost universally. Presently, all tuberculins are manufactured and standardized with Tween 80.Ī person who has been exposed to the bacteria is expected to mount an immune response in the skin containing the bacterial proteins. Tween 80 is a detergent added to tuberculin to prevent its adsorption on glass or plastic surface. ![]() Other tuberculins available in the market are not standardized. PPD-RT 23 with Tween 80 of strength 1 TU and 2 TU are standardized tuberculins available in India supplied by the Bacillus Calmette-Guérin (BCG) vaccine Laboratory, Guindy, Chennai. It is PPD-RT (Research Tuberculin) 23 that is commonly used Indian clinician, are not easily available and may have different interpretation parameters.Ī standard dose of five tuberculin units (TU) (0.1ml) is injected intradermally (into the skin) and read 48 to 72 h later. fortuitum and PPD-Y from the yellow photochromogen M. avium PPD-G from the Gause strain of schotochromogen PPD-B from the nonphotochromogen Battey bacilli PPD-F from the rapid grower M. atypical) mycobacterium are identified by a letter other than S. The “old tuberculin” is no longer used for this purpose instead, a more standardized product called PPD-S (purified protein derivative, prepared according to the method described by Siebert, from M. The tuberculin most widely used is purified protein derivative (PPD), which is derived from cultures of M. The distribution of results generally falls into one of two patterns depending on the rate of false-positive (cross-reactions from other mycobacterial infections) in the population. Consequently, its application in any group of patients will usually yield a wide range of results, from the presence of a reaction in uninfected children to the complete absence of a reaction in some children with confirmed TB disease. However, various factors both in the host and inherent in the test lower both its specificity and sensitivity. After such a long history it is surprising that the interpretation of the test remains controversial. It was developed by Koch in 1890 but the intradermal technique currently in use was described in 1912 by Charles Mantoux, a French physician who developed on the work of Koch and Clemens von Pirquetto to create his test in 1907. tuberculosis infection in an individual and is used in the diagnosis of TB in individual patients, as well as in epidemiological settings, to measure the prevalence of tuberculous infection in populations. Short of demonstrating viable organisms in body tissues and fluids the tuberculin skin test (TST) is the only method of detecting M. A combination of factors including high costs, limited resources and the poor performance of various diagnostic tests make the diagnosis of TB difficult in developing countries. More tests-such as a chest X-ray, a sputum culture, or both-are usually done to see if you have an active TB infection.Tuberculosis (TB) remains a leading cause of morbidity and mortality in the world, especially in developing countries. It also can't tell the difference between a TB infection and a TB vaccination ( BCG vaccination). The test can't tell whether you have active or inactive (latent) TB. No firm bump forms at the test site, or a bump forms that is smaller than 5 mm (0.2 in.)Ī firm bump that is 5 mm (0.2 in.) or larger in size suggests a TB infection.Ī positive reaction can usually be seen for about 1 week.Ī positive tuberculin skin test doesn't mean you have contagious (active) TB. People at lower risk for having TB need to have a larger bump to be diagnosed with a TB infection. If you are at higher risk, a smaller bump is considered a sign of infection. ![]() ![]() Results of the test depend on your risk for TB. Your doctor will consider your chance of having TB when looking at the skin test site. The size of the firm bump (not the red area) is measured 2 to 3 days after the test to find out the result. A firm red bump may mean you have been infected with TB bacteria at some time. Redness alone at the skin test site usually means you haven't been infected with TB bacteria.
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