Tuberculosis (TB) tests are diagnostic tools used to identify Mycobacterium tuberculosis infection. Many people wonder if these tests can cause sickness. While most reactions to TB tests are mild and localized, understanding the different test types and their typical responses clarifies what to expect.
Understanding TB Test Types
Two primary types of tests detect TB infection: the Tuberculin Skin Test (TST) and Interferon-Gamma Release Assays (IGRAs). The TST, also known as the Mantoux test or PPD test, involves injecting a small amount of purified protein derivative (PPD) from the TB bacteria into the top layer of skin, usually on the inner forearm. This test assesses if the immune system reacts to the bacterial proteins. A healthcare professional checks the injection site 48 to 72 hours later for a reaction.
Interferon-Gamma Release Assays (IGRAs) are blood tests, such as QuantiFERON-TB Gold Plus (QFT-Plus) and T-SPOT.TB. IGRAs involve drawing a blood sample from a vein for laboratory analysis. In the lab, blood is mixed with TB-related proteins to observe immune cell reaction by interferon-gamma release. This method typically requires only one patient visit and is not affected by prior BCG vaccination, which can cause false positives with the TST.
Expected Reactions and Mild Symptoms
The Tuberculin Skin Test (TST) commonly causes localized reactions at the injection site. These responses are part of the immune system’s expected reaction to the injected proteins. Individuals may observe redness, swelling, itching, or tenderness. A small, firm bump or wheal typically forms immediately after the injection and may linger for a while. These localized reactions do not indicate illness and usually resolve without intervention.
Less common, but possible, are mild systemic symptoms following a TST. These can include a low-grade headache, mild body aches, or a slight fever. Such symptoms are rare and transient, typically lasting no more than a day or two. The TST does not introduce live bacteria, so it cannot cause a TB infection.
For Interferon-Gamma Release Assays (IGRAs), reactions are minimal, as it is a blood draw. Common responses are localized to the blood draw site. This might include mild soreness, bruising, or a small amount of bleeding. These minor effects are typical of any blood collection procedure. Overall, neither test typically causes a person to feel unwell or sick.
When to Contact a Healthcare Provider
While most reactions to TB tests are mild, specific situations warrant contacting a healthcare provider. Seek medical attention if you experience signs of a severe allergic reaction, which are rare. These signs include difficulty breathing, hives, a widespread rash, or dizziness. Swelling of the face, lips, or throat also indicates a serious reaction requiring immediate care.
Additionally, contact a healthcare provider if the injection site for a TST develops significant or rapidly worsening pain, swelling, blistering, or an open sore. While some local reaction is normal, an unusually severe or spreading reaction should be evaluated. Any systemic symptoms, such as a high fever, persistent body aches, or feeling unwell that lasts for more than a couple of days, also warrant a call to your provider. These instances, though infrequent, require professional assessment for appropriate management.