Tuberculin skin testing fact sheet

Tuberculin Skin Testing
What is It?
How is the TST Read?
The Mantoux tuberculin skin test (TST) is the
The skin test reaction should be read between 48 standard method of determining whether a person is and 72 hours after administration. A patient who infected with Mycobacterium tuberculosis. Reliable does not return within 72 hours will need to be administration and reading of the TST requires standardization of procedures, training, supervision, andpractice.
The reaction should be measured in millimeters ofthe induration (palpable, raised, hardened area orswelling). The reader should not measure erythema How is the TST Administered?
(redness). The diameter of the indurated area shouldbe measured across the forearm (perpendicular to The TST is performed by injecting 0.1 ml of tuberculin purified protein derivative (PPD) into the inner surfaceof the forearm. The injection should be made with atuberculin syringe, with the needle bevel facing upward.
How Are TST Reactions Interpreted?
The TST is an intradermal injection. When placedcorrectly, the injection should produce a pale elevation of Skin test interpretation depends on two factors: the skin (a wheal) 6 to 10 mm in diameter.
„ Measurement in millimeters of the induration„ Person’s risk of being infected with TB and of Classification of the Tuberculin Skin Test Reaction
An induration of 5 or more
An induration of 10 or more
An induration of 15 or more
millimeters is considered positive in
millimeters is considered positive in
millimeters is considered positive in
– Persons with clinical conditions that day of prednisone for 1 month orlonger, taking TNF-alpha antago- What Are False-Positive Reactions?
What is a Boosted Reaction?
Some persons may react to the TST even though they In some persons who are infected with M. tuberculosis, are not infected with M. tuberculosis. The causes of the ability to react to tuberculin may wane over time.
these false-positive reactions may include, but are not When given a TST years after infection, these persons may have a false-negative reaction. However, the TST „ Infection with nontuberculosis mycobacteria may stimulate the immune system, causing a positive, or boosted reaction to subsequent tests. Giving a second „ Incorrect method of TST administration TST after an initial negative TST reaction is called two- Why is Two-Step Testing Conducted?
What Are False-Negative Reactions?
Two-step testing is useful for the initial skin testing of Some persons may not react to the TST even though adults who are going to be retested periodically, such as they are infected with M. tuberculosis. The reasons for health care workers or nursing home residents. This these false-negative reactions may include, but are not two-step approach can reduce the likelihood that a boosted reaction to a subsequent TST will be „ Cutaneous anergy (anergy is the inability to misinterpreted as a recent infection.
react to skin tests because of a weakenedimmune system) Can TSTs Be Given To Persons
„ Recent TB infection (within 8-10 weeks of Receiving Vaccinations?
Vaccination with live viruses may interfere with TST reactions. For persons scheduled to receive a TST, Recent live-virus vaccination (e.g., measles and Either on the same day as vaccination with live- Some viral illnesses (e.g., measles and chicken At least one month after smallpox vaccination „ Incorrect method of TST administration„ Incorrect interpretation of reaction Additional Information
American Thoracic Society and CDC. Diagnostic Who Can Receive a TST?
standards and classification of tuberculosis in adultsand children. Am J Respir Crit Care Med 2000; 161. contraindicated only for persons who have had a severereaction (e.g., necrosis, blistering, anaphylactic shock, or CDC. Guidelines for preventing the transmission of ulcerations) to a previous TST. It is not contraindicated Mycobacterium tuberculosis in health-care settings, for any other persons, including infants, children, 2005. MMWR 2005; 54 (No. RR-17). pregnant women, persons who are HIV-infected, or persons who have been vaccinated with BCG.
CDC. Mantoux Tuberculin Skin Test: Training Materi-als Kit (2003).
How Often Can TSTs Be Repeated?
CDC. Targeted tuberculin testing and treatment of In general, there is no risk associated with repeated latent tuberculosis infection. MMWR 2000; 49 (No.
tuberculin skin test placements. If a person does not return within 48-72 hours for a tuberculin skin test reading, a second test can be placed as soon as possible.
There is no contraindication to repeating the TST, unlessa previous TST was associated with a severe reaction.


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