Targeted Tuberculin Testing and Interpreting Tuberculin
Skin Test Results
||Tuberculin Skin Testing
Last Updated: May 2005
Targeted tuberculin testing is used to focus program activities,
provider practices, and financial resources on groups at the highest
risk for latent tuberculosis infection (LTBI). Once TB disease has
been ruled out, those who would benefit from treatment of LTBI should
be offered this option regardless of their age.
Every effort should be made to test only those persons at the highest
risk, interpret tuberculin skin test (TST) reactions accurately,
and ensure appropriate treatment and completion of the recommended
Persons at Risk for Developing TB Disease
Generally, persons at high risk for developing TB disease fall
into two categories: those who have been recently infected, and
those with clinical conditions that increase the risk of progression
from LTBI to TB disease.
Recent infection should be suspected in the following:
- Close contacts of a person with infectious TB
- Persons who have immigrated from areas of the world with high
rates of TB
- Children < 5 years of age who have a positive TST
- Recent converters (those with an increase of 10 mm or more
in size of TST reaction within a 2-year period)
- Groups with high rates of M. tuberculosis transmission,
such as homeless persons, injection drug users, and persons with
- Persons who work or reside with people who are at high risk
for TB in facilities or institutions such as hospitals, homeless
shelters, correctional facilities, nursing homes, and residential
homes for those with HIV
Clinical conditions that increase the risk of progression from
LTBI to TB disease:
- HIV infection
- Radiographic evidence of prior TB
- Low body weight (> 10% below ideal)
- Diabetes mellitus
- Chronic renal failure or being on hemodialysis
- Jejunoileal bypass
- Solid organ transplant
- Head and neck cancer
- Prolonged use of immunosuppressive agents (e.g., prednisone,
Criteria for Classifying Positive TST Reactions
Reaction of > 5 mm of induration is considered positive in
- HIV-infected persons
- Recent contacts of infectious TB cases
- Persons with fibrotic changes on chest radiograph consistent
with prior TB
- Organ transplant recipients
- Persons who are immunosuppressed for other reasons (e.g., taking
the equivalent of >15 mg/day of prednisone for 1 month or more,
taking TNF-α antagonists)
Reaction of > 10 mm of induration is considered positive in
- Recent immigrants (within last 5 years) from a high-prevalence
- Injection drug users
- Residents or employees of high-risk congregate settings
- Mycobacteriology laboratory personnel
- Children < 4 years of age, or children or adolescents exposed
to adults at high risk
- Persons with clinical conditions previously mentioned
Reaction of > 15 mm of induration is considered positive
- Persons with no known risk factors for TB*
* Although skin testing programs should be conducted only
among high-risk groups, certain individuals may require TST for
employment or school attendance. An approach independent of risk
assessment is not recommended by CDC or the American Thoracic Society.
Questions often arise about the interpretation of TST results in
persons with a history of Bacille Calmette-Guérin (BCG) vaccine,
HIV infection, and recent contacts to an infectious TB case.
BCG vaccine is currently used in many parts of the world to protect
infants and children from severe TB disease, especially TB meningitis.
It does not confer lifelong immunity, and its significance in persons
receiving the TST causes confusion in the medical and lay community.
- History of BCG vaccine is NOT a contraindication for tuberculin
- TST reactivity caused by BCG vaccine generally wanes with time
- If more than 5 years have elapsed since administration of BCG
vaccine, a positive TST reaction is most likely a result of M.
Persons who are HIV infected have a much greater risk for progression
to TB disease if they have LTBI.
- Individuals with HIV infection may be unable to mount an immune
response to the TST and may have false-negative TST results
- Usefulness of anergy testing in TST-negative persons who are
HIV infected has not been demonstrated
Persons with a postive TST result who are contacts of an individual
with infectious TB should be treated regardless of age.
- Some TST-negative persons should also be considered for treatment
(i.e., young children, immunosuppressed)
- Repeat TST in 8–12 weeks if initial test result is negative.
A delayed-type hypersensitivity response to tuberculin is detected
2–12 weeks after infection
tuberculin testing and treatment of latent tuberculosis infection.
MMWR 2000;49 (No. RR- 6).
Adverse Event Data and Revised American Thoracic Society/CDC Recommendations
Against the Use of Rifampin and Pyrazinamide for Treatment of Latent
Tuberculosis Infection. MMWR 2003; 52 (No. 31).
Associated with Blocking Agents Against Tumor Necrosis Factor -
Alpha - California, 2002–2003. MMWR 2004; 53 (No.
of tuberculosis. MMWR 2003; 52(No. RR-11).
Education and Training Resources website
Organization (WHO) website
The following resources can be viewed and downloaded from the CDC
website at www.cdc.gov/tb.