what is a tb mantoux test

3 min read 13-03-2025

The Mantoux tuberculin skin test, also known as the Mantoux test or PPD (purified protein derivative) test, is a simple procedure used to screen for tuberculosis (TB) infection. It doesn't diagnose active TB disease, but it helps identify individuals who have been exposed to the Mycobacterium tuberculosis bacteria and may have latent TB infection (LTBI). Understanding what this test entails is crucial for managing potential TB exposure.

What Does the TB Mantoux Test Detect?

The Mantoux test doesn't detect active TB disease. Instead, it checks for an immune response to the bacteria that causes tuberculosis. If you've been exposed to TB bacteria, your body may develop an immune response, even if you're not currently sick. This immune response is what the test measures. A positive result suggests you've been exposed, and further testing is necessary to determine if you have LTBI or active TB.

Latent TB Infection vs. Active TB Disease

It's vital to understand the difference:

Latent TB infection (LTBI): You have the TB bacteria in your body, but it's not active. You're not contagious and generally don't experience symptoms. However, LTBI can progress to active TB disease later in life.
Active TB disease: The bacteria are active, multiplying, and causing illness. You can spread the bacteria to others through coughing and sneezing. Symptoms include persistent cough, fever, night sweats, and weight loss.

How is the Mantoux Test Performed?

The test involves a small injection of tuberculin (PPD) just under the skin of your forearm. A small bump will form at the injection site. You'll return 48-72 hours later for a healthcare professional to measure the bump (induration).

Reading the Mantoux Test Results

The size of the hardened area (induration) determines the test result:

Positive: A larger area of induration indicates a positive result, suggesting possible exposure to TB bacteria. The size threshold for a positive result varies depending on several factors, including your risk factors for TB, and should be interpreted by a healthcare professional.
Negative: A small or no hardened area indicates a negative result, meaning no significant immune response to TB bacteria was detected.
Indeterminate: Sometimes, the result may be indeterminate, requiring further evaluation.

Important Note: A positive Mantoux test does not mean you have active TB disease. Further testing, such as a chest X-ray and/or sputum culture, is necessary to confirm a diagnosis of active TB.

Who Should Get a Mantoux Test?

The Centers for Disease Control and Prevention (CDC) recommends the Mantoux test for specific groups, including:

Individuals with high-risk exposure to TB: This includes healthcare workers, those living with someone who has active TB, and those residing in areas with high TB prevalence.
Immigrants and refugees from high-TB-burden countries.
People with weakened immune systems (HIV/AIDS, cancer, diabetes).
Children exposed to individuals with active TB.

What are the Limitations of the Mantoux Test?

While the Mantoux test is a valuable screening tool, it does have limitations:

False positives: Certain conditions, like prior BCG vaccination (a TB vaccine common in many parts of the world), can lead to false positive results.
False negatives: A negative test doesn't completely rule out TB infection, especially in individuals with weakened immune systems.

What Happens After a Positive Mantoux Test?

A positive Mantoux test necessitates further evaluation to determine if you have LTBI or active TB disease. Your doctor will likely order additional tests, such as:

Chest X-ray: To check for abnormalities in your lungs.
Sputum culture: To check for the presence of TB bacteria in your sputum (phlegm).

Based on these results, your doctor will determine the appropriate course of action, which might include treatment for LTBI to prevent it from progressing to active TB.

Conclusion

The Mantoux test plays a crucial role in TB screening. Understanding its purpose, procedure, and limitations is essential for interpreting the results and managing potential TB infection appropriately. If you have concerns about TB exposure, consult your doctor for appropriate testing and advice. Remember, early detection and treatment are key to preventing the spread of TB and protecting your health.