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Understanding Lab Values > Tuberculosis (TB) Screening and Testing

Tuberculosis (TB) Screening and Testing

Tuberculosis.jpgWho is screened for tuberculosis?

  • Tuberculosis testing is not recommended in all children, but screening of all children with specific risk questions can identify those in need of testing is recommended at least yearly. We will ask these questions during well visits at 6, 12, 18, and 24 months, and then at yearly well visits.
  • Risks of TB include being in a country outside of the US, Canada, Australia, New Zealand, and Western Europe for more than 1 week or being exposed to someone who has tuberculosis.
  • The CDC has a poster of how the PPD is placed here.

What testing is done?

  • The Tuberculin Skin Test (TST) is the most common test in those found to be at-risk but without symptoms. A small amount of liquid is injected into the forearm. The person returns in 48-72 hours to have the area read. Redness may be normal, but a raised area is measured to read the test.

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  • Blood testing is the preferred test in children older than 4 years who have been immunized against BCG and may be done in other children as well, depending on indications.
  • The type of testing done is determined by the risk factors and medical history of the patient.

What does a positive TB test mean?

  • A positive test means that a person has been exposed to TB germs sometime during his life. It does not indicate that a person has TB active disease or is contagious.

When are TB test results available?

  • The skin test should be examined (or read) 48-72 hours after it is administered. This requires a return visit to our office. Patients do not need an appointment for a nurse to read it. If the nurse is concerned that the area might indicate a positive test, you will be asked to check your child in to the walk in clinic to have a provider do an exam and determine a plan of action. A skin test of 10 mm or more is positive at any time, but smaller bumps might be positive depending on risk levels. (Note: only the bump is read, not the redness).
  • Blood testing is done at the laboratory of your insurance company's choice. We typically get results within about a week. Parents will be called about any positive tests. If the test is negative and the child is registered on our website, notification may be done through our secure messaging portal. If you do not hear from us within 10 days, please call the office during business hours. 

Should a person who has had BCG vaccination get a TB test?

  • Yes. Not all BCG vaccinations are effective. A history of BCG vaccination is important to let us know though. We interpret the results of the test differently in people with this vaccine. A prior BCG vaccine might lead us to order a blood test instead of a skin test. 

What is TB infection?

  • A person with a positive test and normal X-ray has TB infection. This is NOT contagious if there are no symptoms. This is called latent infection and is an opportunity to treat the infection before it becomes active. 

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 do not aerosolize or cough up their germs into the air. 

What will happen if the test is positive?

  • All children with a positive test for tuberculosis will get a chest x-ray to see if there are signs of lung involvement. We must notify the Health Department so they can help identify all contacts. We will refer to an Infectious Disease specialist for guidance on management and treatment.

Why do children without active TB need to be treated?

  • Children with a positive test but no symptoms have latent disease. They can remain in this stage for a very long time. They do not have any symptoms and they do not spread the disease to others.
  • If TB remains untreated in the body, it may activate at any time. Typically this happens when the body's immune system is compromised, as with old age or another illness. Appropriately treating the TB before it causes active disease is beneficial for the long term.

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