The Mantoux test is used to detect tuberculosis, an infectious disease caused by mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis is a relatively common disease that usually affects the lungs, but it may also affect other organ systems and can be deadly.
Many people infected with TB bacteria are asymptomatic and thus have a latent TB infection. Ten percent of latent TB infections will eventually become active TB, with a greater than 50% mortality rate. The Mantoux test is used to diagnose those with a latent TB infection. Once individuals are diagnosed with latent TB infection, treatment may begin which will substantially reduce the chance that a latent TB infection progresses to disease. The detection and treatment of latent TB infection is essential in controlling and potentially eliminating tuberculosis.
Individuals who have been immunized for TB, have had a past cleared TB infection or are infected with a nontuberculous mycobacteria will respond to the Mantoux test similarly to those who have a latent infection, thus the Mantoux test must be interpreted with caution and if a positive result occurs, detailed history should be discussed. Recent scientific advances have led to the development of a more highly specific test for TB infection that may eventually replace the Mantoux test as it is less likely to show a response in individuals who have been immunized for TB or infected with a nontuberculous mycobacteria.
The Mantoux test is also known as the PPD test. PPD stands for Purified Protein Derivative. PPD is an antigen that is taken from dead tuberculosis bacteria. The test is administered by using. 1ml or 5 Tuberculin units of PPD. The solution is injected into the skin of the underside of the forearm with a small needle. A small raised bump forms where the solution is administered and the health care professional should mark two edges of the raised bump to mark the injection site. The bacteria that causes tuberculosis produces a delayed hypersensitivity reaction. Within 48-72 hours after the administration of the test, an individual who has been exposed to the bacteria usually reacts to the PPD antigen in the skin of the injection area. The reaction will cause a raised hardened area or induration, at the site of the injection. The size of this area is measured and the measurement of the induration together with the patient’s risk factors will determine if the result is considered positive.
In preparation for the test, it is important to remember that the results of the test need to be read by the healthcare provider 48-72 hours after the test is administered. The follow-up visit to have the test read should be planned before having the test administered. The healthcare provider should be notified if any surgeries or medical procedures are planned after the test or if a patient has allergies, is pregnant or breastfeeding. Lastly, the test should be postponed if the patient has a skin rash or sunburn on the underside of the forearms.
It is important not to scratch, rub or press on the injection site, nor should one use ointments, lotions or sunscreen on the site, until after the test results have been read by the healthcare provider.
Some people who are infected with tuberculosis may not have a reaction to the PPD test. This is called a false-negative result. Conversely, some people who are not infected with Mycobacterim Tuberculosis may have a positive PPD test result. This is called a false-positive result. For these reasons, the patient’s medical history needs to be carefully taken into account for proper test result interpretation.
Typically a negative reaction, where there is no induration present, or the induration measurement is below the cut-off for the particular patient’s risk category, would indicate that the patient does not have a latent TB infection. There are different cut-offs for the measurement of an induration for different groups of people. If an induration is present and is greater than or equal to 5 mm, this result would be considered positive in individuals who are HIV positive or who are immunosuppressed for other reasons, have had recent contact with people who have TB, or those who have had a chest x-ray that shows changes consistent with TB. If an induration is present and is greater than or equal to 10mm, this result is considered positive in patients who are recent immigrants from areas where TB has a high incidence, IV drug users, individuals who live or work in high-risk settings, have medical conditions that place them at high risk or children under the age of four. If an induration is present and is greater than or equal to 15mm, this is considered positive for any individual, even those with no known risk factors.
Segen, J.C. and J. Wade. Patient’s Guide to Medical Tests: Everything You Need to Know About the Tests Your Doctor Orders. New York, Checkmark Books, 2002.
Rothel, JS., P. Anderson. “Diagnosis of latent Mycobacterium tuberculosis infection: Is the demise of the Man-toux test imminent?”Expert Review of Anti Infective Therapy 3(6) (2005):981–983.
“Mantoux Tuberculosis Skin Test Facilitator Guide.” Centers for Disease Control and Prevention. National Center for HIV, STD and TB Prevention, Division of Tuberculosis Elimination. 1600 Clifton Road, MS E10, Atlanta, GA 30333. (404)639-8140. www.cdc.gov/tb/pubs/Mantoux/guide.htm.
Renee Laux, M.S.
The Mantoux test is a skin test used to identify individuals who have previously been infected with Mycobacterium tuberculosis, the bacterium responsible for tuberculosis infection and disease in humans. The test is performed by injecting 0.1 ml of a solution that contains an extract of cultures of the bacterium, called tuberculin, into the dermis layer of the skin of the forearm with a 27-gauge needle. In individuals who previously have been infected with the bacterium, either clinically or subclinically, the test may stimulate a reaction (called "delayed hypersensitivity reaction") if the body's immune system recognizes the antigenic components in the test solution. The skin reaction is "read" forty-eight to seventy-two hours after the injection by measuring the amount of induration (swelling) at the injection site in millimeters. The sensitivity and the specificity of the test depend upon many variables, and false negative results are common.
John L. Stauffer
(see also: Tuberculosis )
American Thoracic Society (2000). "Diagnostic Standards and Classification of Tuberculosis in Adults and Children." American Journal of Respiratory Critical Care Medicine 161:1376–1395.