How Do Doctors Screen for a Tuberculosis (TB) Infection?
Doctors use two primary Screening methods to check if a person has been infected with the bacteria that causes Tuberculosis (TB): the TB Skin Test (TST) and the TB Blood Test (IGRA). The TST, which involves injecting a small amount of testing fluid (tuberculin) under the skin, requires patients to return 48 to 72 hours later to have the resulting skin reaction (induration) measured by a healthcare professional.
The IGRA is an Alternative, requiring only a single blood draw that is then sent to a laboratory, offering results that are typically ready within 24 to 48 hours. Both tests measure the immune system's reaction to the bacteria; a positive result indicates an infection is present - either latent (inactive and non-contagious) or active (symptomatic and contagious). If the initial screening test is positive, further evaluation, such as a chest X-ray and sputum culture, is immediately required to determine the status of the infection and ensure proper, often long-term, antibiotic treatment is provided to prevent the disease's progression and transmission.
Choosing the right Test depends on patient factors, including prior BCG vaccination history, which can sometimes cause a false positive result with the TST, making the blood test (IGRA) a preferred and more specific option in those cases.
