The Mantoux test, also known as the Tuberculin Skin Test (TST) or PPD test, serves as a common diagnostic tool in public health. It is a screening method primarily used to identify individuals exposed to the bacteria that cause tuberculosis (TB). This test plays a significant role in early detection, helping to manage the spread of TB infection.
Understanding the Mantoux Test
The Mantoux test specifically detects a person’s immune response to components of Mycobacterium tuberculosis, the bacterium responsible for TB. This test helps determine if exposure has occurred, even if the person does not have active disease.
The test utilizes a purified protein derivative (PPD), a substance derived from the TB bacteria. A positive reaction indicates the immune system has encountered TB bacteria, leading to a delayed-type hypersensitivity response. This response is characteristic of either a latent TB infection (LTBI), where the bacteria are present but inactive, or active TB disease.
How the Test is Performed
The Mantoux test involves an injection of PPD. A healthcare professional administers 0.1 milliliters of the PPD solution into the inner surface of the forearm. This intradermal injection places the fluid just beneath the top layer of the skin, creating a small, pale bump or “wheal” at the injection site.
After the injection, leave the site undisturbed. Individuals should avoid touching, scratching, or covering the area with bandages. The test site is then examined by a trained healthcare provider after a specific waiting period. This reading must occur between 48 and 72 hours following the injection, allowing the immune system time to react.
Interpreting Your Results
Interpreting the Mantoux test results involves measuring the induration, which is a firm, raised area at the injection site. This measurement, taken across the forearm, indicates the immune system’s reaction. Redness around the site, known as erythema, is not measured. A trained healthcare professional must perform this reading to ensure accuracy.
A positive result signifies that the body has been infected with TB bacteria, but it does not necessarily mean active TB disease. The size of induration considered positive can vary based on an individual’s risk factors. For instance, an induration of 5 millimeters or more is considered positive for individuals with weakened immune systems, recent close contacts of active TB cases, or those with chest X-ray findings suggestive of previous TB.
An induration of 10 millimeters or more is generally considered positive for people born in countries where TB is common, individuals who misuse drugs or alcohol, and those living or working in high-risk communal settings. For all other individuals without specific risk factors, an induration of 15 millimeters or more typically indicates a positive result. A negative result, characterized by no significant induration, suggests that the person has likely not been infected with TB bacteria.
Next Steps After a Positive Result
If a Mantoux test yields a positive result, further diagnostic steps are usually recommended to determine if the individual has active TB disease or a latent infection. These steps commonly include a chest X-ray to examine the lungs for signs of active disease, and sputum tests for active bacteria in respiratory samples.
If active TB disease is ruled out through these additional tests, treatment for latent TB infection (LTBI) may be advised. Treatment for LTBI aims to prevent the dormant bacteria from becoming active and causing disease. Common treatment regimens often involve short courses of rifamycin-based medications, such as isoniazid and rifapentine for three months, or daily rifampin for four months. Consulting a healthcare provider is important for personalized advice and to develop an appropriate treatment plan.