what is mantoux test

3 min read 14-03-2025

The Mantoux test, also known as the tuberculin skin test (TST) or PPD test (purified protein derivative), is a simple, inexpensive screening test used to identify whether a person has been infected with Mycobacterium tuberculosis, the bacteria that causes tuberculosis (TB). It doesn't directly diagnose active TB disease, but rather indicates past exposure to the bacteria. Understanding what the Mantoux test is and what it means is crucial for effective TB management.

How the Mantoux Test Works

The test involves injecting a small amount of tuberculin (a purified protein derivative of M. tuberculosis) just under the skin of your forearm. A tiny bubble will appear at the injection site. You'll return 48-72 hours later for a healthcare professional to measure the reaction. This reaction, or lack thereof, determines the test result.

Reading the Mantoux Test Results

The healthcare provider will measure the diameter of any raised, hardened area (induration) at the injection site in millimeters (mm). The size of the induration, along with factors like your risk for TB, determines the interpretation of the test. A larger induration generally suggests a higher likelihood of past exposure to the M. tuberculosis bacteria.

Interpreting Induration Size:

Positive Result: A positive result doesn't automatically mean you have active TB. It suggests you've been exposed to the bacteria and have developed an immune response. Further testing is needed to determine if you have latent TB infection (LTBI) or active TB disease.
Negative Result: A negative result usually indicates that you haven't been infected with M. tuberculosis.
Indeterminate Result: Sometimes, the result is indeterminate. This might happen due to improperly performed testing or other factors. Your healthcare provider will discuss the next steps if your result is indeterminate.

What a Positive Mantoux Test Means

A positive Mantoux test only signifies that you've been exposed to the TB bacteria, not that you have active TB disease. This exposure might lead to:

Latent TB infection (LTBI): The bacteria are present in your body, but they're not actively causing disease. You're not contagious and usually don't experience symptoms. However, LTBI can progress to active TB disease, particularly if your immune system is weakened.
Active TB disease: This is the stage where the bacteria actively multiply and cause illness. Symptoms can include cough (often with blood), chest pain, weakness, weight loss, and fever. Active TB is contagious and requires treatment to prevent its spread.

Who Needs a Mantoux Test?

Certain individuals are at a higher risk of contracting TB and may be recommended for a Mantoux test:

People with close contact with individuals diagnosed with TB.
Individuals living in areas with high rates of TB.
Healthcare workers.
Immigrants from countries with high TB prevalence.
People with weakened immune systems (e.g., HIV/AIDS patients).
Residents of long-term care facilities.

Further Investigations After a Positive Mantoux Test

If your Mantoux test is positive, your doctor will likely order further tests to determine if you have LTBI or active TB disease. These tests might include:

Chest X-ray: To check for abnormalities in the lungs.
Sputum culture: To detect the presence of TB bacteria in your sputum (phlegm).
Interferon-gamma release assays (IGRAs): Blood tests that can help distinguish between LTBI and active TB disease.

The Mantoux Test: A Crucial Tool in TB Screening

The Mantoux test remains a vital tool in identifying individuals who have been exposed to the Mycobacterium tuberculosis bacteria. While not a diagnostic test for active TB, it's a crucial first step in screening and managing TB cases, helping prevent the spread of this potentially serious disease. Remember to discuss your results and any concerns with your healthcare provider. They can provide personalized advice based on your individual risk factors and test results.