What Does a Positive TB Test Look Like?
Introduction
Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis. It primarily affects the lungs, but it can also affect other parts of the body, such as the kidneys and spine. Early detection and treatment of TB are crucial to prevent the spread of the disease and its complications. One way to detect TB is through TB testing. In this article, we will discuss what a positive TB test looks like.
What is a TB Test?
A TB test is a test used to detect TB infection. There are two types of TB tests:
Mantoux Tuberculin Skin Test (TST)
The Mantoux TST is the most common TB test. It involves injecting a small amount of purified protein derivative (PPD) into the skin on the forearm. The area is then observed for a reaction.
Interferon-Gamma Release Assays (IGRAs)
IGRAs are blood tests used to detect TB infection. They measure the amount of interferon-gamma released by the body in response to TB antigens.
What Does a Positive TB Test Mean?
A positive TB test means that a person has been infected with TB bacteria. It does not necessarily mean that the person has active TB disease. Instead, it indicates that the person has been exposed to the bacteria and their immune system has reacted to it.
A positive TB test result can also be an indication of latent TB infection (LTBI), which means the bacteria are present but the person is not sick and does not have any symptoms. However, if left untreated, LTBI can progress to active TB disease.
What Does a Positive Mantoux TST Look Like?
The Mantoux TST is read 48 to 72 hours after the injection. A positive Mantoux TST looks like a raised, red bump at the injection site. The size of the bump is measured in millimeters. In general, a bump of 5 mm or more is considered positive for people with an increased risk of TB, such as those with HIV or recent contact with someone with TB. A bump of 10 mm or more is considered positive for people who have other risk factors for TB, such as healthcare workers and people who live in crowded or congregate settings. A bump of 15 mm or more is considered positive for people who have no known risk factors for TB.
It is important to note that a positive Mantoux TST can result in false-positive results. This means that the test can show positive even if the person does not have TB. False-positive results can occur due to a previous BCG vaccination or exposure to non-tuberculous mycobacteria.
What Does a Positive IGRA Look Like?
IGRAs are read in a laboratory, and a positive result means that the person has been infected with TB bacteria. The results are reported as either positive or negative. A positive IGRA does not distinguish between LTBI and active TB disease.
A positive IGRA indicates that the person has been infected with TB bacteria and has mounted an immune response. The result is based on the amount of interferon-gamma released in response to TB antigens. The higher the amount, the more likely it is that the person has TB infection.
False-positive results can occur with IGRAs, but they are less common than with the Mantoux TST.
What to Do if You Have a Positive TB Test
If you have a positive TB test, it is important to follow up with additional testing to determine if you have active TB disease or LTBI. Your healthcare provider may recommend a chest X-ray or sputum culture to check for active TB disease.
If you have LTBI, your healthcare provider may recommend treatment to prevent the development of active TB disease. Treatment usually involves taking medication for several months. It is important to take all medication as prescribed, even if you start feeling better before the medication is finished.
If you have active TB disease, your healthcare provider will prescribe medication to treat the disease. Treatment usually involves taking medication for six to nine months. It is important to take all medication as prescribed and to follow up with your healthcare provider regularly to ensure that the treatment is working.
If you have a positive TB test, it is also important to inform close contacts, such as family members, friends, and coworkers, so that they can be tested for TB infection.
Conclusion
A positive TB test indicates that a person has been infected with TB bacteria. It is important to follow up with additional testing to determine if the person has active TB disease or LTBI. Treatment is available for both conditions. If you have a positive TB test, it is important to inform close contacts so that they can be tested for TB infection as well. Early detection and treatment of TB are crucial to prevent the spread of the disease and its complications.
