A TB test is conducted to determine whether you have been exposed to the Mycobacterium tuberculosis complex, the bacteria responsible for causing TB. Two distinct methods are employed to screen for latent tuberculosis infection (LTBI): the TB skin test and the TB blood test. Both forms of TB tests, including the skin test and blood test, function by gauging your immune system's response to antigens extracted from the Mycobacterium tuberculosis bacterium, which causes TB. Antigens are substances that trigger your immune system to generate antibodies as a defense mechanism. This denotes that your immune system encounters an unfamiliar element and is striving to counteract it. The mechanism behind a TB skin test entails evaluating your immune system's reaction to a purified protein derivative (PPD) solution that is injected beneath your skin. PPD is a protein derived from the TB-causing bacteria. It's important to note that this isn't live bacteria and won't cause illness. If you've previously been exposed to TB bacteria, your skin will exhibit a response to the antigens, manifesting as a solid, red bump at the injection site within three days. Conversely, a TB blood test involves laboratory scientists blending your blood sample with antigens and controls, then employing an immunoassay method to gauge the reaction. Your results will be interpreted as negative, positive, or indeterminate based on this reaction.