Norm of Mantoux Skin Test (PPD Test, Purified Protein Derivative Test, TB Test, Tuberculin Skin Test, TST, Tuberculosis Test)
The appropriate criterion for defining a positive skin test reaction depends on the population being tested. For adults and children with HIV infection, close contacts of infectious cases, and those with fibrotic lesions on chest radiograph, a reaction of ≥5 mm is considered positive. For other at-risk adults and children, including infants and children younger than 4 years of age, a reaction of ≥10 mm is positive. Persons who are unlikely to be infected with Mycobacterium tuberculosis should generally not be skin tested. If a skin test is performed on a person without a defined risk factor for tuberculosis infection, ≥15 mm is positive.
Normal finding; lack of redness or induration of skin at site of skin test; zone of redness and induration <5 mm.
Usage of Mantoux Skin Test (PPD Test, Purified Protein Derivative Test, TB Test, Tuberculin Skin Test, TST, Tuberculosis Test)
Screening is used to identify infected persons at high risk of disease who would benefit from preventive therapy and to find persons with clinical disease in need of treatment. As a screening tool, tuberculin skin testing is the standard method of identifying persons infected with active M. tuberculosis. It is indicated for clients with signs suggestive of current tuberculosis (TB) disease (such as abnormality in mediastinum on radiograph) or symptoms (such as cough, hemoptysis, weight loss); recent contact with clients with confirmed or suspected cases of TB; clients with abnormal chest radiographs compatible with past TB; clients with medical conditions that increase the risk of TB (such as diabetes, immunosuppressive therapy, AIDS); groups at high risk for developing TB. For clients with previous BCG vaccination or in clients at risk for latent TB infection, the CDC as of 2005 no longer recommends Mantoux testing, and instead recommends use of newer interferon tests. (See RD1-interferon tests for tuberculosis—Blood .)
Description of Mantoux Skin Test (PPD Test, Purified Protein Derivative Test, TB Test, Tuberculin Skin Test, TST, Tuberculosis Test)
An intradermal skin test to detect tuberculosis infection (active or dormant). Tuberculin, a protein fraction of tubercle bacilli, is injected intradermally in the human. A localized thickening with redness indicates an accumulation of small, sensitized lymphocytes, which occurs as a result of active or dormant tuberculosis. Clients at high risk for tuberculosis (HIV-infected persons, the very young and the very old, the malnourished, alcoholics, drug abusers, and the chronically ill) should be screened with the tuberculin skin test. Clients with human immuno deficiency virus infection are at increased risk for developing tuberculosis infection and should be screened with the tuberculin skin test. Other clients at high risk for becoming infected with Mycobacterium tuberculosis include the very young and the very old, those who are malnourished, alcohol and drug abusers, and the chronically ill. Newer interferon tests called “IFN gamma assays” have been approved in Europe and the United states to help detect latent tuberculosis infection. See RD1-interferon tests for tuberculosis—Blood for more information on these tests.
Professional Considerations of Mantoux Skin Test (PPD Test, Purified Protein Derivative Test, TB Test, Tuberculin Skin Test, TST, Tuberculosis Test)
Consent form IS required.
It is not known whether the test can cause fetal harm or affect reproductive capacity.
The test should be given to pregnant women only if clearly indicated. The test should not be given if the client has had a previous positive test.
- Assess for previous history of positive purified protein derivative (PPD) reaction. (The test should not be administered in this case.)
- Obtain a tuberculin syringe and PPD.
- Draw up PPD in a tuberculin syringe, following the manufacturer's directions. Use a ½-inch, 26- or 27-gauge needle.
- Cleanse the injection site on the lower dorsal surface of the forearm with alcohol, and allow the area to dry.
- Stretch the skin taut.
- Inject intradermally 0.1 mL of a solution containing 0.5 tuberculin unit of PPD. Injection should be made with a disposable needle and syringe just under the surface of the skin, with the needle bevel facing upward to provide a discrete, pale elevation of the skin (a wheal) 6 to 10 mm in diameter. Discard used needles and syringes in a puncture-resistant container (do not recap needles).
- Mark the test area to locate it for reading.
- Read the test area 48–72 hours later. Examine the site, using good light. Inspect the skin for induration. Induration ≥5 mm diameter generally indicates infection. Rub lightly from the area of normal skin to the indurated area. Circle the induration with a pencil.
- An induration of ≥5 mm diameter should be interpreted as a positive reaction if the client has known contact with an individual with active tuberculosis or if there is a chest radiograph with findings consistent with tuberculosis. Isoniazid therapy is recommended to decrease the risk of developing the disease in positive reactors.
- A chest radiograph is necessary with all positive reactions.
- Epinephrine hydrochloride solution (1:1000) should be readily available for use in the event of anaphylaxis.
Client and Family Teaching
- The skin test does not distinguish between current disease and past infection.
- The skin test should not be administered to known tuberculin-positive reactors because of the possibility of severe reactions (vesiculation, ulceration, and necrosis).
Factors That Affect Results
- Tuberculin must be stored as recommended by the manufacturer. Tuberculin solution should be stored between 2 and 8 degrees C (35 and 46 degrees F). It should be exposed to light only when being withdrawn and administered. An open vial may be used only for 1 month.
- Subcutaneous rather than intradermal injection will nullify the test.
- Cross-reactions with nontuberculous mycobacteria may cause false-positive results.
- Serial testing may cause false-positive results.
- Vaccination with the bacille Calmette-Guérin (BCG) has a variable effect on the skin test reaction. However, a history of BCG vaccination should not alter interpretation of the skin test. The newer RD1-interferon tests for tuberculosis—Blood are the test of choice instead of Mantoux testing for these clients.
- False-negative reactions may occur in the following instances: bacterial infections, immunologic defects, immunosuppressive agents, live virus vaccinations (BCG, measles, mumps, polio, and rubella), malnutrition, old age, overwhelming tuberculosis, renal failure, and viral infections (chickenpox, measles, and mumps).
- False-negative results can occur, even in the presence of active TB, whenever sensitized T lymphocytes are temporarily depleted in the body.
- See also RD1-interferon tests for tuberculosis—Blood.