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Tuberculosis (TB) is a highly contagious disease caused by the bacteria Mycobacterium tuberculosis. It primarily affects the lungs but can also impact other parts of the body such as the kidneys, spine, or brain. TB remains a significant global health problem, and early detection is crucial for effective treatment and prevention of its spread. This article explores how a tuberculosis test works, providing answers to frequently asked questions.
What is a tuberculosis test, and why is it necessary?
A tuberculosis test is performed to determine if a person has been infected with the bacteria that cause TB. It is crucial to identify infected individuals as early as possible to prevent the disease from progressing and to curb its transmission. Timely diagnosis allows for appropriate treatment, reducing the risk of complications and containing the infection’s spread in the community.
How does a tuberculosis test work?
There are two primary types of tuberculosis tests: the tuberculin skin test (TST) and the interferon-gamma release assay (IGRA).
What is a tuberculin skin test (TST)?
The TST, also known as the Mantoux test, involves injecting a small amount of purified protein derivative (PPD) into the skin of the forearm. PPD contains antigens derived from the bacteria that cause tuberculosis. If a person has been infected with TB, the skin around the injection site will develop a raised, red bump called an induration within 48 to 72 hours.
How is the TST result interpreted?
The size of the induration is measured and interpreted based on specific guidelines. The interpretation takes into account factors such as age, underlying medical conditions, and the individual’s risk of exposure to TB. A positive TST result indicates that the person has been infected with TB bacteria at some point. However, it cannot distinguish between active and latent infections.
What is an interferon-gamma release assay (IGRA)?
The IGRA is a blood test that measures the release of interferon-gamma, a chemical produced by the immune system when it is exposed to TB antigens. The blood sample is mixed with TB-specific antigens, and if the person has been infected with TB, the immune cells present in the blood will release interferon-gamma.
How is the IGRA result interpreted?
Like the TST, the IGRA provides information about TB infection but does not differentiate between active and latent forms. The test result is determined by measuring the amount of interferon-gamma released in response to TB antigens. A positive result suggests the person is infected with the bacteria that cause tuberculosis.
Which test is more accurate, the TST, or the IGRA?
Both tests have their advantages and limitations. While the TST is widely available and less expensive, it may produce false-positive results due to previous BCG vaccination or exposure to non-tuberculosis mycobacteria. On the other hand, the IGRA is more specific and less susceptible to false-positive results but can be affected by factors such as an inadequate immune response.
In conclusion, tuberculosis tests play a crucial role in diagnosing and managing this infectious disease. Whether through the tuberculin skin test or the interferon-gamma release assay, these tests provide valuable information about a person’s TB infection status. However, it is important to note that these tests alone cannot confirm active disease or rule out latent infection. Therefore, individuals with positive results should undergo further evaluations, including chest X-rays and sputum tests, to accurately diagnose and treat tuberculosis.
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