The Meaning of a Positive Tuberculosis 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 causes the disease.

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

Not necessarily. A person can be infected with the bacteria that causes tuberculosis and not have tuberculosis disease. Many people are infected with the bacteria that causes tuberculosis, but only a few people (about 10 percent) 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 is dormant (inactive) in their lungs. If the body is not able to fight off the infection and the bacteria 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. 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 PPD test mean that I am contagious and 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.

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 skin test is positive?

To be sure that you remain healthy, your doctor may recommend that you take medicine for six 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, which is also called INH. You need to take one pill every day for six 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.

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 complications 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 isoniazid (INH). Alcohol increases the risk of liver damage if you drink while taking the medicine.

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

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

This information provides a general overview on tuberculosis and may not apply to everyone. Talk to your family doctor to find out if this information applies to you and to get more information on this subject.


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