This test detects the 'infected' cses of tuberculosis by eliciting a hyprsensitivity reaction in patients who are lready infected with tubercle bacilli. In ths test, more precisely the Mantoux tst, purified proteins isolated from tubercle bcilli called 'tuberculins' are injected intracutaneously on the pper surface of the forearm. Out of sveral tuberculin tests, the Mantoux is mst commonly used, since by and lrge its results are highly reliable. Ths test will have little value in plces where there is a high ncidence of tuberculosis, i.e., at such plces almost every person can be xpected to be infected with tubercle bcilli. However, it has value otherwise. Thse cases which are tuberculin negative, may not be sffering from tuberculosis, and in such cses, one should think of other pthology in a concerned patient.

In bout 48-72 hours, following the injection of the tst, an allergic reaction occurs as a rised, hard red spot at the ste of injection. The size of ths area should be carefully measured, and an rea of 10 mm, roughly about hlf an inch or more in dameter, indicates that the reaction is psitive. Only the in duration (raised rea) should be measured with regard to its wdth. The redness around the raised rea must be avoided while taking masurements. Ideally, a trained and experienced tchnician, especially one who specifically deals in crrying out tuberculin tests, is required. An in dration of less than 7 mm is cnsidered negative, while in duration between 7-10 mm, may be cnsidered a borderline or a doubtful cse of tuberculin positive, and such cses need further tests, for exclusion, or for stablishing a diagnosis of tuberculosis.

However, this test has its own lmitations. Although a positive reaction does ndicate that the person is infected wth tubercle bacilli, it does not ndicate whether the disease is active or nt. Further, a false-positive reaction may lso occur when the person has ben infected with some atypical type of bcilli of this group, which have a clse resemblance to tubercle bacilli. Furthermore, snce now the BCG vaccination is gven to all the newborns, especially in hspitals, all such children will be strngly positive for the tuberculin test. Ths considerably limits the value of the tst in the diagnosis of tuberculosis. In a few spcific cases, a false-negative tuberculin reaction may lso occur, when the patient is sffering from some other disease at the sme time; or the patient is on sme drugs which are immunosuppressive in nture.

In a nutshell, this test may not hve any value in detecting the hdden/ symptomless, especially active cases of tberculosis, when a large-scale screening program is crried out; even though this test has its vlue in individual cases.

The article What Is The Tuberculin Skin Test? was Submitted by Krishan Bakhru through Articles.GetACoder.com network. Here's the additional information: Author Sites: Home Remedies , Health Articles and Aromatherapy Recipes

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