TB Testing

Two Step TB Testing

Potential Indications for TB 2-Step (Booster) Testing

TB 2-Step testing is recommended by the Centers for Disease Control (CDC) as a baseline test for health care workers and other selected populations who have the possibility of exposure to tuberculosis as part of their student or work experience. TB 2-Step testing is done in order to get an accurate baseline TB test prior to contact with the public or patients that could have active TB.

If a person has had previous unknown infection with tuberculosis and it has been more than a year since their last TB test, it is possible for their TB test to read negative even though they have been infected. This is due to the waning of the antibody response after infection. However, receiving the TB test will stimulate the antibodies and another test done shortly within a week or the first test will demonstrate the TB infection by being read as positive or reactive.

About the TB 2-Step (Booster) Test

The most common procedure for TB 2-Step testing is to give the first Mantoux test (PPD). If the test is negative, repeat the PPD in one week and have the repeat test read in 48-72 hours or 2-3 days. If the second PPD is negative, the baseline TB 2-Step test is negative.

Positive PPD Reactions & Chest X-Rays

If you have a positive PPD, it doesn't mean that you have Tuberculosis. A positive PPD means that your body's immune system recognizes the TB protein injected into your arm and is mounting an antibody response. This is why you have a raised red area at the site of injection. This reaction shows that you have been exposed to the germ that causes Tuberculosis. The exposure may be recent or may have occurred years ago. A positive test may, but does not indicate the presence of active Tuberculosis disease. Therefore, once you have had a positive skin test, you should thereafter receive a chest X-ray, or health clearance to demonstrate no active Tuberculosis.

Some people immunized in countries with a high incidence of TB were given the BCG vaccine and may test positive as a result. However, even with a history of BCG vaccination, a positive test is still a positive test.

DO NOT HAVE ANY MORE SKIN TESTS AFTER YOU HAVE TESTED POSITIVE (>10-15mm). Whether you have an active disease or not, you will always test positive.

PLEASE NOTE: Students who tested positive for their TB skin test at the student health center will require a chest-xray clearance within two (2) weeks of the TB skin test was read to demonstrate no active Tuberculosis. Failure to provide chest-xray clearance will result on a temporary HOLD on student's registration.

What is Tuberculosis?

Tuberculosis (TB) is a disease caused by bacteria called Mycobacterium tuberculosis. The bacteria usually attack the lungs. But, TB bacteria can attack any part of the body such as the kidney, spine, and brain. If not treated properly, TB disease can be fatal.

How TB Spreads

TB is spread through the air from one person to another. The TB bacteria are put into the air when a person with TB disease of the lungs or throat coughs, sneezes, speaks, or sings. People nearby may breathe in these bacteria and become infected.

TB is NOT spread by

• shaking someone’s hand
• sharing food or drink
• touching bed linens or toilet seats
• sharing toothbrushes
• kissing

What Are Latent TB Infections?

People who are not sick have what is called latent TB infection. People who have latent TB infection do not feel sick, do not have any symptoms, and cannot spread TB to others. But, some people with latent TB infection go on to get TB disease.

People with active TB disease can be treated if they seek medical help. Even better, most people with latent TB infection can take medicine so that they will not develop active TB disease.

In most people who breathe in TB bacteria and become infected, the body is able to fight the bacteria to stop them from growing. The bacteria become inactive, but they remain alive in the body and can become active later. This is called latent TB infection. People with latent TB infection

• have no symptoms
• don't feel sick
• can't spread TB to others
• usually have a positive skin test reaction or QuantiFERON-TB Gold test (QFT-G)
• may develop active TB disease if they do not receive treatment for latent TB infection

Many people who have latent TB infection never develop active TB disease. In these people, the TB bacteria remain inactive for a lifetime without causing disease. But in other people, especially people who have weak immune systems, the bacteria become active and cause TB disease.

What Are Active TB Infections?

TB bacteria become active if the immune system can't stop them from growing. The active bacteria begin to multiply in the body and cause active TB disease. The bacteria attack the body and destroy tissue. If this occurs in the lungs, the bacteria can actually create a hole in the lung. Some people develop active TB disease soon after becoming infected, before their immune system can fight the TB bacteria. Other people may get sick later, when their immune system becomes weak for another reason.

Babies and young children often have weak immune systems. People infected with HIV, the virus that causes AIDS, have very weak immune systems. Other people can have weak immune systems, too, especially people with any of these conditions:

• substance abuse
• diabetes mellitus
• silicosis
• cancer of the head or neck
• leukemia or Hodgkin's disease
• severe kidney disease
• low body weight
• certain medical treatments (such as corticosteroid treatment or organ transplants)
• specialized treatment for rheumatoid arthritis or Crohns disease

Symptoms of TB depend on where in the body the TB bacteria are growing. TB bacteria usually grow in the lungs. TB in the lungs may cause symptoms such as

• a bad cough that lasts 3 weeks or longer
• pain in the chest
• coughing up blood or sputum (phlegm from deep inside the lungs)

Other symptoms of active TB disease are

• weakness or fatigue
• weight loss
• no appetite
• chills
• fever
• sweating at night