CS228419_I

National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention 

Division of Tuberculosis Elimination

(Page 1 of 2)

TB Elimination

Targeted Tuberculosis Testing and 

Interpreting Tuberculin Skin Test Results

Introduction

Targeted tuberculosis (TB) 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 and TB blood test results 

accurately, and ensure appropriate treatment and 

completion of the recommended regimen.

Table 1: Criteria for Classifying Positive TST 

Reactions

Positive IGRA result or a TST reaction of 5 or more 

millimeters of induration is considered positive in

» HIV-infected persons

» Recent contacts of a TB case

» Persons with fibrotic changes on chest radiograph

consistent with old 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 longer, taking TNF-α antagonists)

Positive IGRA result or a TST reaction of 10 or more 

millimeters of induration is considered positive in

» Recent immigrants (< 5 years) from high-prevalence

countries

» Injection drug users

» Residents and employees of high-risk congregate settings

(e.g., correctional facilities, nursing homes, homeless

shelters, hospitals, and other health care facilities)

» Mycobacteriology laboratory personnel

» Children under 4 years of age, or children and adolescents

exposed to adults in high-risk categories 

Positive IGRA result or a TST Reaction of 15 or more 

millimeters of induration is considered positive in

» 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.

Persons at Risk for Developing TB 

Disease

Generally, persons at high risk for developing TB 

disease fall into two categories: those who have an 

increased likelihood of exposure to persons with 

TB disease, and those with clinical conditions that 

increase the risk of progression from LTBI to TB 

disease.

Persons at risk for exposure to persons with TB 

disease include:

• Close contacts of a person with infectious TB

disease

• Persons who have immigrated from areas of the

world with high rates of TB

• Residents and employees of high-risk

congregate settings (e.g., correctional facilities,

homeless shelters, health care facilities)

Persons more likely to progress from LTBI to TB 

disease include:

• Recent converters (those with an increase of

10 mm or more in size of TST reaction within a

2-year period)

• HIV-infected persons

• Young children who have a positive TST result

• Those with a history of prior, untreated TB or

fibrotic lesions on chest radiograph

• Injection drug users

• Those receiving TNF-α antagonists for treatment

of rheumatoid arthritis or Crohn’s disease

Clinical conditions that increase the risk of 

progression from LTBI to TB disease:

• HIV infection

• Low body weight (>10% below ideal)

• Silicosis

• Diabetes mellitus
• Chronic renal failure or being on hemodialysis

• Gastrectomy

• Jejunoileal bypass

• Solid organ transplant

• Head and neck cancer

Special Considerations

Questions often arise about the interpretation 

of TST results in persons with a history of Bacille 

Calmette-Gurin (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 skin testing

• 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. tuberculosis infection

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 positive 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 8-10 weeks if initial test result

is negative. A delayed-type hypersensitivity

response to tuberculin is detected 2–8 weeks

after infection

Additional Information

1. ATS/CDC. Targeted tuberculin testing and

treatment of latent tuberculosis infection.

MMWR 2000;49 (No. RR- 6). http://www.cdc.

gov/mmwr/preview/mmwrhtml/rr4906a1.

htm

2. Targeted Tuberculosis (TB) Testing and

Treatment of Latent TB Infection (slide

set). http://www.cdc.gov/tb/publications/

slidesets/LTBI/default.htm

3. ATS/CDC. Update: 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). http://www.cdc.gov/mmwr/

preview/mmwrhtml/mm5231a4.htm

4. CDC. Tuberculosis Associated with Blocking

Agents Against Tumor Necrosis Factor -

Alpha - California, 2002–2003. MMWR 2004;

53 (No. 30). http://www.cdc.gov/mmwr/

preview/mmwrhtml/mm5330a4.htm

5. ATS/CDC. Treatment of tuberculosis. MMWR

2003; 52(No. RR-11). http://www.cdc.gov/

mmwr/preview/mmwrhtml/rr5211a1.htm

6. TB Education and Training Resources

website http://www.findtbresources.org/

7. World Health Organization (WHO) website

http://www.who.int/en/

8. CDC Division of TB Elimination website

http://www.cdc.gov/tb

9. Treatment of Latent Tuberculosis Infection:

Maximizing Adherence (factsheet). http://

www.cdc.gov/tb/publications/factsheets/

treatment/LTBIadherence.htm

10. Treatment Options for Latent Tuberculosis

Infection (factsheet). http://www.cdc.gov/

tb/publications/factsheets/treatment/

LTBItreatmentoptions.htm

http://www.cdc.gov/tb

December 2011