The TB Skin Test: What to Expect During Administration
Receiving a tuberculosis (TB) skin test, known as the Mantoux tuberculin skin test (TST), involves a quick and generally tolerable procedure. A healthcare professional uses a very small needle to inject a tiny amount of liquid, called tuberculin purified protein derivative (PPD), just beneath the top layer of skin on the forearm. This shallow injection creates a small, pale bump, often called a wheal, which looks somewhat like a mosquito bite. The sensation is a brief pinch or slight sting, and the minimal discomfort quickly subsides.
The needle used for the TST is fine and short, designed for intradermal injections, meaning it does not go deep into muscle or veins. This technique ensures the PPD remains in the superficial layer of the skin, necessary for accurate observation of the body’s immune response. The entire administration process is very fast, taking less than a minute. Following the injection, the small wheal disappears within a few hours, leaving behind a slight raised area.
After the TB Skin Test: What to Expect
After the TB skin test is administered, it is common to experience minor reactions at the injection site. You might notice some mild redness, a small raised area, or a slight itch. These reactions are normal and do not necessarily indicate a positive test result; they are simply the body’s local response to the injection. It is important to leave the injection site undisturbed to ensure an accurate reading. Avoid scratching, rubbing, or applying any creams, lotions, or bandages to the area.
You will need to return to a healthcare provider to have the test site read within 48 to 72 hours after the injection. This specific time frame is important for accurately interpreting the reaction. During this follow-up appointment, the healthcare professional will measure the diameter of any raised, hardened area (induration) at the site, not just the redness. The presence and size of this induration determine whether the test result is considered positive or negative, indicating potential exposure to TB bacteria.
Understanding Other TB Testing Methods
Beyond the skin test, other methods exist for detecting tuberculosis, each with a different experience regarding discomfort. Interferon-Gamma Release Assays (IGRAs) are blood tests, such as the QuantiFERON-TB Gold Plus or T-SPOT.TB test, that can identify TB infection. These tests involve a standard blood draw, similar to what you might experience for other routine blood work. The discomfort associated with a blood draw is a brief pinch or sting as the needle enters the vein, followed by a dull pressure.
Another diagnostic tool, particularly for active TB disease in the lungs, is a chest X-ray. This imaging procedure is non-invasive and causes no physical pain. You simply stand or lie still for a few moments while the X-ray images are taken. While a chest X-ray does not directly test for the presence of the TB bacteria, it can reveal changes in the lungs consistent with TB disease.