Tuberculosis Testing

Childhood Infections

A doctor looking at a chest xray.
A chest x-ray will be done if your child has a positive TB test. Photo © istockphoto

Tuberculosis, or TB, is a life-threatening infection caused by the Mycobacterium tuberculosis bacterium.

Your kids can get tuberculosis if they are around someone who has active tuberculosis disease who coughs or sneezes near them. They are not likely to get TB through more casual contact, such as shaking hands or even sharing a drink.

Tuberculosis Testing

TB testing is no longer routinely recommended for all children.

Instead of universal TB testing, only those children who have risk factors for tuberculosis are usually tested now. This includes:

  • having close contact with someone who has active TB disease.
  • immigrating from an area of the world that has high rates of TB, which is why a TB test is recommended after an international adoption, especially if the adoption was from a country in Latin America and the Caribbean, Africa, Asia, Eastern Europe, or Russia.
  • children with HIV infection or other conditions that weaken their immune system
  • children with symptoms of active TB disease, including a chronic cough, especially if it lingers for three weeks or longer and is productive of blood or sputum, chest pain, weight loss, fever, and/or night sweats, etc.
  • living where active TB might be common, such as a homeless shelter, prison or jail, or migrant farm camp.
  • teens who inject illegal drugs.

If necessary, these children will usually have a TB blood test, or more commonly, a TB skin test (Mantoux tuberculin skin test) or PPD.

This TB test is then read after 48 to 72 hours to see if the person has a reaction and has TB. Keep in mind that a positive TB test can show a reaction from 5 to 10 mm or even 15 mm and be positive, depending on if the child has HIV (5 mm), is less than 4 years old or is a recent immigrant from a high risk area (10 mm), or if there are no other risk factors, then it might be 15 mm or more to be positive.

A TB test is also sometimes required before doing volunteer work in a hospital or zoo (to protect the animals).

TB Blood Tests

TB blood tests are becoming a little more popular as they have a few benefits, including that:

  • they don't have to be read after 48 to 72 hours, which typically requires a return visit to the doctor
  • they are the preferred test for people who have had a BCG vaccine, as the TB vaccine can make later TB tests hard to interpret

Positive Tuberculosis Test

It is important to keep in mind that a positive TB skin test does not necessarily mean that your child has an active case of tuberculosis.

The next step is a chest x-ray or sputum sample. Depending on these results, your child may either have a latent TB infection or active TB disease, which is contagious to others. Either way, treatment will be necessary. The big difference will be how many TB drugs your child will need to take and for how long.

While a latent TB infection might require just four to nine months of treatment with a single drug, such as Rifampin or Isoniazid, active TB disease will usually require treatment with three or four medications for eight weeks and then two medications for another 18 to 31 weeks.


CDC. Tuberculosis Fact Sheets. Accessed November 2011.

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