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TB Skin Testing:
Questions and Answers (FAQ's)

This section answers general questions about the TB skin test and provides information on skin testing interpretation. For specific information about school-related testing requirements for students and school personnel please refer to School TB Skin Testing Requirements.  If you have questions about non-school employee testing issues, see Employee Skin Testing for Non-School Settings. You can receive a TB test within Los Angeles County by viewing this page, DHS Clinics and Health Centers - TB Skin Testing locations. To assist you, TB Control has provided the following answers to the most frequently asked questions about the TB skin test:  

GENERAL QUESTIONS	ANSWERS
What is a TB skin test?	A "TB Skin Test" is a test to see if TB germs are present in the body. L.A. County uses the Mantoux method only for testing.
Why would someone need a skin test?	A skin test is used to see if a person has been exposed and infected by M. tuberculosis or tubercle bacilli. A test may also be required by an employer as an employment screening or to enter school.
What does a positive TB skin test result mean?	A positive skin test means that a person has been infected with TB germs sometime during that person's life. It does not indicate that a person is contagious or symptomatic.
What should a person do if positive?	A person with a positive reaction requires further evaluation. This person should be referred to a healthcare provider to have a chest x-ray or other clinical exams if indicated.
When should a TB test be examined? (read or checked)	The skin test should be examined (or read) 48-72 hours after it is administered. It is acceptable to read the skin test up to 96 hours after administration if it is not possible to read it earlier. After 96 hours, a skin test of less than 10 mm of induration should be repeated. A skin test of 10 mm or more is positive at any time.
Should a person who had a BCG vaccination get a TB skin test?	Yes. Not all BCG vaccinations are effective. A history of BCG vaccination does not exempt students or employees from the skin test.
What is latent TB infection?	A person with a positive skin test, no symptoms, and a normal X-ray has latent TB infection. This person is NOT contagious.
When is TB contagious?	TB can be contagious in adolescents and adults, who are coughing, have a positive skin test, and an abnormal chest X-ray. TB medications will make the person non-contagious very quickly. Because of the efficacy of TB medicines, patients are not quarantined and are usually able to return to school or work within several weeks.
Are children with active TB contagious?	Children under the age of 12 rarely have contagious TB. This is because they have TB in a different area in the body and do not aerosolize or cough up their germs into the air.
Where can I obtain a skin test?	Your healthcare provider should be able to provide this test or you can contact your nearest DHS Clinics and Community Health Centers.

Remember: 

• People who have a positive TB skin test with a normal chest x-ray are NOT contagious, but may need medicine to prevent them from developing active TB.  

• Children under the age of 12 with active TB are rarely contagious, and generally do not need to be kept out of school. 

If you have any questions please call the Nurse Consultation Unit at the Los Angeles County Department of Health, Tuberculosis Control Program, (213) 744-6160 or (213) 744-6151.

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