A tuberculin skin test (also called a Mantoux tuberculin test) is done to see if
you have ever been exposed to
tuberculosis (TB). The test is done by putting a small
amount of TB protein (antigens) under the top layer of skin
on your inner forearm. If you have ever been exposed to the TB bacteria (Mycobacterium tuberculosis), your skin will react to the
antigens by developing a firm red bump at the site within 2 days.
The TB antigens used in a tuberculin skin test are called purified
protein derivative (PPD). A measured amount of PPD in a shot is put under the
top layer of skin on your forearm. This is a good test for finding a TB
infection. It is often used when symptoms, screening, or testing, such as a
X-ray, show that a person may have TB.
tuberculin skin test cannot tell how long you have been infected with TB. It
also cannot tell if the infection is
latent (inactive) or is active and can be passed to
A tuberculin skin test is done to find
people who have tuberculosis (TB), including:
A tuberculin skin test should not be done for
Before having a tuberculin skin test,
tell your doctor if you:
Talk to your doctor about any concerns you have regarding
the need for the test, its risks, how it will be done, or what the results will
mean. To help you understand the importance of this test, fill out the
medical test information form(What is a PDF document?).
For a tuberculin skin test, you sit
down and turn the inner side of your forearm up. The skin where the test is
done is cleaned and allowed to dry. A small shot of the TB antigen (purified
protein derivative, or PPD) is put under the top layer of skin. The fluid makes
a little bump (wheal) under the skin. A circle may be drawn around the test
area with a pen.
Do not cover the site with a bandage. You must see
your doctor 2 to 3 days after the test to have the skin test checked.
You may feel a quick sting or pinch from
There is a very slight risk of having a severe
reaction to the tuberculin skin test, especially if you have had tuberculosis
allergic reaction can cause a lot of swelling and pain
at the site. A sore may be present.
You cannot get a TB infection
from the tuberculin skin test, because no live bacteria are used for the
Some redness at the skin test site
is expected. The site may itch, but it is important that you do not scratch it,
since this may cause redness or swelling that could make it hard to read the
skin test. If itching is a problem, put a cold washcloth on the site and then
A strong positive reaction may cause mild pain. Talk to
your doctor if you have:
A tuberculin skin test is done to see if
you have ever had
tuberculosis (TB) (infection with Mycobacterium tuberculosis).
Redness alone at the skin test
site usually means you have not been infected with TB bacteria. A firm red bump
may mean you have been infected with TB bacteria at some time. The size of the
firm bump (not the red area) is measured 2 to 3 days after the test to
determine the result. Your doctor will consider your chance of having TB when
looking at the skin test site.
Results of the test depend on your risk for TB. If you are in a high-risk group, a smaller bump is considered a sign of infection. People at low risk for having TB need to have a larger bump to be diagnosed with a TB infection.
Three levels of risk have been defined:
A positive reaction usually remains visible for about 1
No firm bump forms at the test
site, or a bump forms that is smaller than
5 mm (0.2 in.).
A firm bump that is
5 mm (0.2 in.) in size suggests a
TB infection in people who are in a high-risk group.
A firm bump that is
10 mm (0.4 in.) in size suggests a
TB infection in people who are in a moderate-risk group.
A firm bump that is
15 mm (0.6 in.) in size suggests a
TB infection in people who are in a low-risk group.
A positive tuberculin skin test does not mean you have a
contagious (active) infection. The test cannot tell if the infection is active
or inactive (latent TB). It also cannot tell the difference between a TB
infection and a TB vaccination (BCG vaccination). More tests—such as a
chest X-ray, a sputum
culture, or both—are usually done to see if you have
an active TB infection.
Reasons you may not be able to
have the test or why the results may not be helpful include:
Pasipanodya J, et al. (2011). Tuberculosis and other
mycobacterial diseases. In ET Bope et al., eds., Conn's Current Therapy 2011. pp. 295–301. Philadelphia: Saunders.
Other Works Consulted
American Thoracic Society, Centers for Disease Control
and Prevention, Infectious Diseases Society of America (2003). Treatment of
tuberculosis. American Journal of Respiratory and Critical Care Medicine, 167(4): 603–662.
Centers for Disease Control and Prevention (2005).
Guidelines for using the QuantiFERON®-TB test for
diagnosing latent Mycobacterium tuberculosis infection.
MMWR, 54(RR-15): 49–55.
Division of Tuberculosis Elimination, National Center
for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention (2009). Questions and Answers About TB. Available online:
Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
April 4, 2013
E. Gregory Thompson, MD - Internal Medicine
& R. Steven Tharratt, MD, MPVM, FACP, FCCP - Pulmonology, Critical Care Medicine, Medical Toxicology
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