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Tuberculosis: The Meaning of A Positive Test


What is tuberculosis?

Tuberculosis (say: "too-burr-cue-low-sis") also called TB, is an infection caused by a bacteria (a germ). Tuberculosis usually affects the lungs, but it can spread to the kidneys, bones, spine, brain and other parts of the body.

What does it mean if I have a positive test?

The most commonly used skin test to check for tuberculosis is the PPD. If you have a positive PPD, it means you have been exposed to a person who has tuberculosis and you are now infected with the bacteria that cause the disease.

Do I have tuberculosis if I have a positive PPD test?

Not necessarily. A person can be infected with the bacteria that cause tuberculosis and not have tuberculosis disease. Many people are infected with the bacteria that cause tuberculosis, but only a few of these people (about 10%) go on to develop the disease. People who have the disease are said to have "active" tuberculosis.

Healthy people who get infected with the tuberculosis bacteria are able to fight off the infection and do not get tuberculosis disease. The bacteria are dormant (inactive) in their lungs. If the body is not able to fight off the infection and the bacterium continues to grow, active tuberculosis develops.

Would I know if I developed active tuberculosis?

You might not know that you have active tuberculosis. Tuberculosis bacteria can grow in your body without making you feel sick. However, most people with active tuberculosis don't feel well. People with tuberculosis often feel tired and have a cough that won't go away. They may also lose weight, or have a fever, or break out in a sweat in bed (called "night sweats"). They may have trouble breathing.

If you have active tuberculosis, you will have to get regular checkups and chest x-rays for the rest of your life to make sure you stay free of disease, even after you have taken tuberculosis medicine.

Does a positive test mean that I can give tuberculosis to someone else?

Not necessarily. After you have a positive PPD skin test, you must have a chest x-ray and a physical exam to make sure that you don't have active disease and that you're not contagious (able to spread the disease).

It usually takes only a few days to tell whether you're contagious. Most people with a positive skin test aren't contagious.

What will I have to do if my test is positive?

To be sure that you remain healthy, your doctor may recommend that you take medicine for 9 months to kill the tuberculosis infection. If you don't take the medicine, the bacteria will remain in your lungs, and you will always be in danger of getting active tuberculosis. The medicine used to treat tuberculosis infection is isoniazid (say: "eye-so-nye-ah-zid"), which is also called INH. You need to take 1 pill every day for 9 months.

People who take INH may have side effects, but not very often. Side effects include a skin rash, an upset stomach or liver disease. Ask your doctor about other side effects that might happen.

What if I forget to take my medicine?

It is very important that you take the medicine every day. Keep the medicine in a place where you will always see it. Take it at the same time every day. Ask your doctor what to do if you forget to take a pill.

Do I need to do anything else?

Every month you will need to visit your doctor to get another prescription of the medicine you are taking and to be sure you don't have any side effects or problems from the medicine. If you are feeling well, your doctor will give you a prescription for the next month. It is important that you stop drinking alcohol while taking INH. Drinking alcohol while taking the medicine increases your risk of liver damage.

Could I still get active tuberculosis after I take the medicine for 9 months?

Even after you take the medicine every day for 9 months there is a small chance that you could develop active tuberculosis disease, because some bacteria are resistant to the medicine. Staying healthy depends on having sensible living habits. You need enough sleep and exercise and a healthy diet to keep up your health and resistance to the tuberculosis bacteria.

Reviewed/Updated: 09/09
Created: 11/96

This handout provides a general overview on this topic and may not apply to everyone. To find out if this handout applies to you and to get more information on this subject, talk to your family doctor.

Copyright © 1996-2002 American Academy of Family Physicians
Permission is granted to print and photocopy this material for nonprofit educational uses.
Written permission is required for all other uses, including electronic uses.

Revised – 6/13/2012

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Last Updated: 2/4/13