February 18, 2016

From the Desk of Assistant Medical Director,
Ron Lamontagne, MS, APRN, BC:

Tuberculosis, commonly known as TB, is a bacterial infection that can spread through the lymph nodes and bloodstream to any organ in your body. It is most often found in the lungs. Most people who are exposed to TB never develop symptoms because the bacteria can live in an inactive form in the body.

There are two kinds of tests that are used to determine if a person has been infected with TB bacteria: the tuberculin skin test and TB blood tests. A positive TB skin test or TB blood test only tells that a person has been infected with TB bacteria. It does not tell whether the person has latent TB infection (LTBI) or has progressed to TB disease. Other tests, such as a chest x-ray and a sample of sputum, are needed to see whether the person has TB disease.

Tuberculin skin test: The TB skin test (also called the Mantoux tuberculin skin test) is performed by injecting a small amount of fluid (called tuberculin) into the skin in the lower part of the arm. A person given the tuberculin skin test must return within 48 to 72 hours to have a trained health care worker look for a reaction on the arm. The health care worker will look for a raised, hard area or swelling, and if present, measure its size using a ruler. Redness by itself is not considered part of the reaction.

TB blood tests: TB blood tests (also called interferon-gamma release assays or IGRAs) measure how the immune system reacts to the bacteria that cause TB. An IGRA measures how strong a person’s immune system reacts to TB bacteria by testing the person’s blood in a laboratory.

Two IGRAs are approved by the U.S. Food and Drug Administration (FDA) and are available in the United States:

QuantiFERON®–TB Gold In-Tube test (QFT-GIT)
T-SPOT®.TB test (T-Spot)
Positive IGRA: This means that the person has been infected with TB bacteria. Additional tests are needed to determine if the person has latent TB infection or TB disease. A health care worker will then provide treatment as needed.
Negative IGRA: This means that the person’s blood did not react to the test and that latent TB infection or TB disease is not likely.

ExpressMED/BOAC clinics perform the T-SPOT for TB blood testing. Although blood testing for TB is initially more costly than the skin test method the benefits of a blood test are two-fold. Patients who are tested for TB through blood testing are not required to return to the clinic within 72 hours, and employers avoid the risk of missed appointments and having to begin the process all over again. Additionally, blood test results are not subject to visual interpretation and eliminate the occurrence of a false positive read.

If you would like more information and pricing on the T-SPOT method you may contact Meagan Anderson, Practice Manager in Manchester or Kelly St. Louis, Practice Manager in Salem.