Living With Tuberculosis (TB)

Why am I being tested for tuberculosis?
What is the test like?
What additional tests are required if I have a positive skin test?
Who should get tested?
What’s the difference between active and latent TB infections?

Why am I being tested for tuberculosis?

Many places of work or school in the United States and abroad give tuberculosis skin tests. This is a preventative measure designed to limit the spread of active tuberculosis disease. Active TB can be spread through the air and can become a huge public health problem if not immediately identified and treated.

What is the test like?

The most common TB test involves getting a small injection of tuberculin in the skin – usually on the inside of one of your wrists. If you have not been infected with TB, your body’s immune system will not recognize the tuberculin as being harmful and therefore, will not mount an immune response against it. This means that you will not have a bump at the injection site a day or two after the test.

However, if you have ever been infected with TB, or are currently infected with TB, then your immune system will mount a swift response against the tuberculin, and a bump will form at the injection site over the next day or two. The bump is from inflammation – one of the ways your body’s immune system responds to things like germs that make you sick.

It is important to understand that a positive skin test does not necessarily mean that you have active disease – you may have a latent TB infection. A positive skin test means that you’ll have to go through more tests (that is, unless you’ve had the BCG vaccination). These additional tests are required to determine if you have the latent (inactive) or the active form of the disease.

What additional tests are required if I have a positive skin test?

X-Ray

X-rays of your lungs will be taken to assess the extent of the infection. An x-ray of the lungs allows doctors to look for pneumonia, cavities (holes in the lung) or scarring. All can be seen in active tuberculosis disease.

Smear

A smear is a test to see whether there are TB bacteria in your phlegm (mucus coughed up from the lungs). For this test, a lab technician will smear a sample of your phlegm onto a glass slide. Then, a special stain is added to the phlegm that will enable your doctor to see any TB germs under a microscope. Results for this test are usually available in about a day.

QuantiFERON-TB® Gold (QFT)

QuantiFERON-TB® Gold (QFT) is a blood test used to find out if you are infected with TB bacteria. The QFT measures the response to TB antigens (proteins) when they are mixed with a small amount of your blood. This is a new test that some health departments and physicians are using.

Who should get tested?

You should get tested for TB if:

• You think you might have active TB disease.
• You have spent time with a person known to have active TB disease or suspected to have active TB disease.
• You have HIV infection or another condition that puts you at high risk for active TB disease.
• You are from a country where active TB disease is very common (most countries in Latin America and the Caribbean, Africa, Asia, Eastern Europe and Russia).
• You live somewhere in the United States that active TB disease is more common (such as a homeless shelter, migrant farm camp, prison or jail, and some nursing homes).
• You inject illegal drugs.

What’s the difference between active and latent TB infections?

Active TB disease

Active TB disease is an illness where the TB bacteria are multiplying and attacking different parts of your body. The symptoms of active TB disease include weakness, weight loss, fever, no appetite, chills and sweating at night. Other symptoms of active TB disease depend on where in the body the bacteria are growing. If active TB disease is in the lungs (pulmonary TB), the symptoms may include a bad cough, pain in the chest, and coughing up blood. A person with active TB disease may be infectious and spread TB to others.

If you are diagnosed with an active TB disease, be prepared to give a careful, detailed history of every person with whom you have had contact. Since the active form is so contagious, all of these people will need to be tested, as well.

Immediate and aggressive treatment with antibiotics is necessary to treat active TB disease. You may be asked to take your antibiotics under the careful observation of your doctor or other healthcare professional. This is because forgetting to take your medication, or failure to take your medication as prescribed, can lead to the life-threatening condition of multidrug-resistant TB (MDR TB). Treating multidrug-resistant TB requires long hospital stays and high doses of antibiotic medications that often have severe side effects.

Latent TB infection

Latent TB infection is less aggressive than the active form of the disease. A latent TB infection means that your body is infected with live TB germs, but they are not rapidly reproducing and spreading. If you have a latent TB infection, your skin test will usually be positive but you will have no symptoms: you won’t feel sick, and you can't spread TB to others. However, you may develop active TB disease if you do not receive treatment for latent TB infection. Treatment for latent TB infection is usually a single antibiotic for nine months. A long treatment is required because antibiotics only work when the bacteria are actively dividing.

Return to Top

This information has been approved by Gwen Huit, MD (April 2006).