Doctors perform a Mantoux test if you may have been exposed to bacteria that cause tuberculosis (TB). This could be by being around someone with it or traveling to a country where there is a lot of it.

Here’s how the test works: A small amount of protein taken from dead tuberculosis bacteria is placed just under the skin (it’s completely safe). The site of injection is checked two to three days later. If the TB bacteria has been in the person’s body before, it will cause a slightly hard, sometimes red swelling (called “induration”) where the test was placed on the skin.

Whether or not it is a “positive” test depends on the amount of swelling, as measured by a doctor or nurse. It also depends on the child’s circumstances. For example, some swelling may be okay for a healthy older child with no known exposure to tuberculosis. But the same size swelling may be “positive” in a younger child who could possibly have been exposed. This can be confusing. That’s why doctors and nurses are the ones who must look at a person’s arm and review the medical history to decide if the Mantoux test shows a need for therapy.

A “positive” Mantoux test doesn’t always mean someone has TB disease. It just means that the bacteria have been in the body at some time. Your daughter’s doctor will check her to look for any signs of TB. The next step is to get an X-ray of the chest to check for TB infection in the lungs.

The checkup and X-ray are normal most of the time. Even if they are, doctors might still recommend medicine when the Mantoux is positive. That’s because there is the possibility that the TB bacteria that made it into the body could begin to grow over time and cause disease in the lungs or elsewhere. Of course, if anything is not normal on the chest X-ray, your daughter would be prescribed a combination of medicine to cure her.

Therapy for a true new positive Mantoux test lasts six to nine months, depending on the prescribed drug and the medical facts. Isoniazid, which is taken daily for nine months, is prescribed most commonly. Your doctor will do some blood tests and want to see your daughter regularly to watch for any side effects. It’s very important that she take ALL of the medication as directed. Otherwise it may not work. And the TB bacteria could continue to grow.

Once the Mantoux is positive it stays positive, even after treatment.