TUBERCULIN SKIN TESTING
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The Mantoux tuberculin skin test is the only preferred method of testing patients for latent tuberculosis infections. An intradermal injection of 0.1 ml of purified protein derivative (PPD), which contains 5 tuberculin units, is applied to the forearm. Trained health care workers should read the reaction 48 to 72 hours after the injection. If the patient fails to return before 72 hours, a positive result can be interpreted up to 1 week after the injection; however, if the result is negative after 72 hours, the test should be repeated.It is the diameter of induration, and not the diameter of erythema, that determines the result of the tuberculin skin test. The diameter of induration perpendicular to the long axis of the forearm should be recorded. Interpretation of the result is dependent upon the size of the induration and the characteristics of the patient.Tuberculin testing in patients with a prior history of bacillus Calmette-Guerin vaccination is not contraindicated. In these patients, the tuberculin skin test should be interpreted in the same fashion as patients without prior vaccination, and the prior history of bacillus Calmette-Guerin vaccination should be ignored for purposes of interpreting the skin test.Two-stage skin testing should be considered in instances in which patients are tested regularly. The reactivity to the skin testing may decrease over time but may be boosted by regular skin testing. If this effect is unrecognized, a patient may be incorrectly classified as a recent converter. If the first tuberculin skin test result is negative or is reactive but less than 10 mm in diameter, a repeat skin test in 1 week is recommended. If the skin test is greater than or equal to 10 mm at that time, the patient is not considered a recent converter.Anergy panels are no longer used in the interpretation of the results, even in those infected with HIV. Patients with HIV who have a negative tuberculin skin test and a negative anergy panel result do not benefit from treatment with isoniazid. The results of a negative anergy panel, therefore, do not aid in the decision of treatment. In patients with no known risk factors, a reaction greater than or equal to 15 mm is considered positive. However, targeted testing programs should exclude these patients from being tested.*54/348/5*
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