CS 320275-C September 2020

Tuberculin Skin Testing

What is it?

The Mantoux tuberculin skin test (TST) is one method 

of determining whether a person is infected with 

Mycobacterium tuberculosis. Reliable administration 

and reading of the TST requires standardization of 

procedures, training, supervision, and practice. 

How is the TST Administered?

The TST is performed by injecting 0.1 ml of tuberculin 

purified protein derivative (PPD) into the inner surface 

of the forearm. The injection should be made with a 

tuberculin syringe, with the needle bevel facing upward. 

The TST is an intradermal injection. When placed 

correctly, the injection should produce a pale elevation of 

the skin (a wheal) 6 to 10 mm in diameter. 

How is the TST Read?

The skin test reaction should be read between 48 and 72 

hours after administration by a health care worker trained 

to read TST results. A patient who does not return within 

72 hours will need to be rescheduled for another skin test.

The reaction should be measured in millimeters of the 

induration (firm swelling). The reader should not measure 

erythema (redness). The diameter of the indurated area 

should be measured across the forearm (perpendicular to 

the long axis). 

How Are TST Reactions Interpreted?

Skin test interpretation depends on two factors:

• Measurement in millimeters of the induration 

• Person’s risk of TB infection or the risk of progression 

to TB disease if infected 

Classification of the Tuberculin Skin 

Test Reaction

• An induration of 5 or more millimeters is considered 

positive in

» People living with HIV

» A recent contact of a person with 

infectious TB disease 

» People with chest x-ray findings 

suggestive of previous TB disease

» People with organ transplants

» Other immunosuppressed people (e.g., patients 

on prolonged therapy with corticosteroids 

equivalent to/greater than 15 mg per day of 

prednisone or those taking TNF-α antagonists)

• An induration of 10 or more millimeters is considered 

positive in

» People born in countries where TB disease is 

common, including Mexico, the Philippines, 

Vietnam, India, China, Haiti, and Guatemala, 

or other countries with high rates of TB

» People who abuse drugs 

» Mycobacteriology laboratory workers

» People who live or work in high-risk congregate 

settings (e.g., nursing homes, homeless 

shelters, or correctional facilities)

» People with certain medical conditions that place 

them at high risk for TB (e.g., silicosis, diabetes 

mellitus, severe kidney disease, certain types 

of cancer, and certain intestinal conditions) 

» People with a low body weight 

(<90% of ideal body weight)

» Children younger than 5 years of age 

» Infants, children, and adolescents exposed 

to adults in high-risk categories

• An induration of 15 or more millimeters is considered 

positive in 

» People with no known risk factors for TB

Information for Health Care Providers
What Are False-Positive Reactions?

Some persons may react to the TST even though they 

are not infected with M. tuberculosis. The causes of these 

false-positive reactions may include, but are not limited to, 

the following: 

• Previous TB vaccination with the bacille CalmetteGuérin (BCG) vaccine 

• Infection with nontuberculosis mycobacteria 

(mycobacteria other than M. tuberculosis)

• Incorrect measurement or interpretation of reaction 

• Incorrect antigen used

A TB blood test is the preferred method of testing for 

people who have received the BCG vaccine in order to 

prevent false-positive reactions. TB blood tests are also 

called interferon-gamma release assays or IGRAs.

What Are False-Negative Reactions?

Some persons may not react to the TST even though they 

are infected with M. tuberculosis. The reasons for these 

false-negative reactions may include, but are not limited to, 

the following: 

• Anergy

• Recent TB infection (within the past 8 to 10 weeks)

• Very young age (younger than 6 months)

• Recent live-virus measles or smallpox vaccination

• Incorrect method of giving the TST

• Incorrect measuring or interpretation of TST reaction

Who Can Receive a TST?

Most persons can receive a TST. TST is the recommended 

method of testing for children younger than 5 years of 

age. It should be noted that the American Academy of 

Pediatrics (AAP) recommends that either a TST or TB 

blood test (interferon-gamma release assay [IGRA]), can be 

used in children 2 years and older. In children previously 

vaccinated with BCG, a TB blood test is preferred to 

avoid a false-positive TST result caused by a previous 

vaccination with BCG.

TST is contraindicated only for persons who have had a 

severe reaction (e.g., necrosis, blistering, anaphylactic 

shock, or ulcerations) to a previous TST. It is not 

contraindicated for any other persons, including infants, 

children, pregnant women, or persons living with HIV. 

However, TB blood tests are the preferred method of testing 

for people who have received the BCG TB vaccine.

How Often Can TSTs Be Repeated?

In general, there is no risk associated with repeated 

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, unless a previous 

TST was associated with a severe reaction. 

What is a Boosted Reaction?

A boosted reaction occurs mainly in previously infected, 

older adults whose ability to react to tuberculin has 

decreased over time. When given a TST years after 

infection, these persons may have an initial negative 

reaction. However, the TST may stimulate the immune 

system, causing a positive or boosted reaction to 

subsequent tests. Giving a second TST after an initial 

negative TST reaction is called two-step testing. 

Why is Two-Step Testing Conducted?

Two-step testing is useful for the initial skin testing of 

adults who are going to be retested periodically, such 

as some health care workers. This two-step approach 

can reduce the likelihood that a boosted reaction will be 

misinterpreted as a recent infection. 

Can TSTs Be Given To Persons 

Receiving Vaccinations?

Vaccination with live viruses, including measles, mumps, 

rubella, oral polio, varicella, yellow fever, BCG, and oral 

typhoid, may interfere with TST reactions. For persons 

scheduled to receive a TST, testing should be done as 

follows:

• Either on the same day as vaccination with live-virus 

vaccine or 

• At least 1 month after the administration of the live-virus 

vaccine 
Are there alternative tests to the TST?

There are two kinds of tests that are used to determine if 

a person has been infected with TB bacteria: the TB blood 

test and the TB skin test. TB blood tests (sometimes called 

IGRAs) use a blood sample to find TB infection. The tests 

measure the response of TB proteins when they are mixed 

with a small amount of blood. Only one visit is required to 

draw blood for this test. Health care providers are encouraged 

to use newer TB blood tests to screen for TB infection. In 

order to prevent false-positive reactions, TB blood tests are 

also the preferred method of TB testing for people 5 years of 

age and older who have received the BCG TB vaccine.

What does a positive TST mean for the 

diagnosis of latent TB infection and TB 

disease?

Diagnosis of Latent TB Infection

A diagnosis of latent TB infection is made if a person has 

a positive TB test result and a medical evaluation does 

not indicate TB disease. The decision about treatment for 

latent TB infection will be based on a person’s chances of 

developing TB disease by considering their risk factors.

Diagnosis of TB Disease

TB disease is diagnosed by medical history, physical 

examination, chest x-ray, and other laboratory tests. TB 

disease is treated by taking several drugs as recommended 

by a health care provider.

What are treatment options for latent 

TB infection?

Treating latent TB infection is effective in preventing TB disease 

and less costly than treating TB disease. There are several 

treatment regimens for the treatment of latent TB infection. 

These regimens use the drugs isoniazid, rifapentine, or 

rifampin. 

CDC and the National Tuberculosis Controllers Association 

(NTCA) preferentially recommend short-course, rifamycinbased, 3- or 4-month latent TB infection treatment regimens 

over 6- or 9-month isoniazid monotherapy (6H or 9H, 

respectively). Short-course regimens include: Three months 

of once-weekly isoniazid plus rifapentine (3HP), four months 

of daily rifampin (4R), or three months of daily isoniazid plus 

rifampin (3HR). Short-course latent TB infection treatments 

are effective, are safe, and have higher completion rates than 

longer treatments. 

If a short-course treatment regimen is not an option, 6H or 9H 

is an effective alternative latent TB infection treatment regimen.

Additional Information

• CDC. Guidelines for preventing the transmission of Mycobacterium tuberculosis in health-care settings, 2005. MMWR 

2005; 54 (No. RR-17). www.cdc.gov/tb/publications/guidelines/infectioncontrol.html

• CDC. Mantoux Tuberculin Skin Test: Training Materials Kit (2003). 

• CDC. Targeted tuberculin testing and treatment of latent tuberculosis infection. MMWR 2000; 49 (No. RR-6). www.cdc.

gov/MMWR/PDF/rr/rr4906.pdf

• Lewinsohn et al., Official American Thoracic Society/Infectious Diseases Society of America/CDC Clinical Practice 

Guidelines: Diagnosis of Tuberculosis in Adults and Children, Clinical Infectious Diseases, 2017, Pages e1–e33. www.

academic.oup.com/cid/article/64/2/e1/2629583

• Latent TB Infection Testing and Treatment: Summary of U.S. Recommendations www.cdc.gov/tb/publications/ltbi/pdf/

CDC-USPSTF-LTBI-Testing-Treatment-Recommendations-508.pdf

• What You Need To Know About the Tuberculosis Skin Test www.cdc.gov/tb/publications/pamphlets/tb_skin_test.pdf

• Patient Education Materials Series www.cdc.gov/tb/education/patient_edmaterials.html

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