Skin Tests

County of Los Angeles Department of Health Services
Public Health Programs - TB Control Program

TB Skin Test Questions and Answers

The incidence of Tuberculosis (TB) disease has increased dramatically in Los Angeles County since 1988. The causes of this increase are many, such as: Human Immunodeficiency Virus (HIV) disease, homelessness, poverty, and the large numbers of persons immigrating to this area from countries with high incidence of TB. Due to the increase of TB cases, the Los Angeles County Department of Health Services has continued to mandate skin tests for first-time school entrants. In addition, California regulations were updated in 1987 to reflect current policies for the screening of school personnel.

To assist the reader, this article will respond to the most frequently asked questions:

What does a positive TB skin test result mean?
  • A positive skin test means that a person has been exposed to TB germs sometime during his life. It does not indicate that a person has TB or is contagious.
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 do 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 TB infection?
  • A person with a positive skin test and normal X-ray has TB infection. This 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 efficiency 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 lung and do not aerosolize or cough up their germs into the air. It is for this reason that the Los Angeles County Department of Health Services has been instructed to check the immunization record on these children as being free of communicable TB on the day that the X-ray is taken.
If a student or staff member is found to have active TB, what does the County Health Department do?
  • Not all TB is contagious. If the health department determines that the student or staff member is contagious, they will not be allowed to remain in school, and the persons sharing the air space with this person will be tested for TB. The student or staff will not be allowed back to school until they are no longer contagious.
I read about this new strain of TB where the drugs do not work. Am I in danger of getting this?
  • There really is not a new strain. There have always been people in which some of the medicines do not work. If this is the case, we use additional medicines and give them for a longer time. Cases where medicines are not completely effective are uncommon in Los Angeles County.


In Los Angeles County, what students must have a TB test?
  • At enrollment, all kindergarten entrants and all students grades 1-12 who never previously attended a California school. They must provide written documentation of a TB test using the Mantoux technique. Kindergarten entrants must have had this test within the year prior to the first day of school
My child attended school in California and left the country for several years. Does he need a skin test when he returns?
  • No. Students who previously attended a California school are exempt from the requirement, even if they have never had a skin test.
My child is transferring from another school within California. Does he need a skin test?
  • No. Students entering at any grade level from any other California school (public, private, or parochial) are exempt from the requirement even if they never received a skin test.
Can my child attend school with a new positive skin test?
  • Yes. A student can enter a school after the skin test is read by the school nurse or the family's health provider in the community. A student can be conditionally admitted for up to 20 school days until a negative X-ray result or a notation from the family's health provider is received stating that the student is free of communicable TB. If the school does not receive the documentation, the child may be excluded from school
It's against my personal beliefs for my child to have a skin test. Can my child still enter school?


  • Yes. Personal belief exemptions are allowed. The parent may sign the personal belief statement on the back of the California School Immunization Record (CSIR) card.
In the past, my child had a positive skin test and/or took medication for TB prescribed by our doctor. What do I need to bring to school to allow him/her to be enrolled?
  • A child with a previous positive skin test must bring documentation from a health care provider of previous skin test results, X-ray, treatment if any, and a current statement from a health care provider that he/she is free of communicable TB.
What type of TB screening must employees undergo?
  • The Mantoux Tuberculin Skin Test is the only acceptable method of TB screening for school employees.
Which volunteers need a TB test ?
  • Volunteers who have repeated contact with students in the classroom setting must meet the same criteria for TB testing as staff. Exception: Volunteers who come in to assist with one time activities, such as: clerical functions, supervising field trips, or dances do not have sufficient contact with students or staff to constitute a risk.
How often does a TB test have to be repeated?
  • If you have a negative skin test, you need a repeat test at least every four years. If you have a documented positive skin test, you must have an initial chest X-ray. After that, you still need to be screened every four years. You must present, either a certificate from a health provider stating that you are free from communicable TB, or have your chest
  • X-ray repeated.
Why aren't people who work with children (teachers, school aides, etc.) required to have TB screening more often?
  • Minimum state regulations require TB screening every 4 years. School staff may request TB testing more frequently from their health care provider, but school districts are not required to provide it more than every 4 years.
I had a positive TB skin test many years ago, but can't find my records. Why can't I just get a chest X-ray?
  • If you cannot document in writing a previous positive skin test (from your own records or your physician), you will have to get another skin test. Only the skin test will demonstrate TB infection.



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