what is mantoux test

3 min read 13-03-2025

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 determine if a person has been infected with Mycobacterium tuberculosis, the bacteria that causes tuberculosis (TB). It doesn't diagnose active TB disease, but rather indicates whether you've been exposed to the bacteria at some point in your life.

How the Mantoux Test Works

The test involves a small amount of tuberculin solution being injected just under the skin of your forearm. This solution contains a purified protein derivative from the TB bacteria.

Reading the Test Results

You'll return to your doctor or healthcare provider 48-72 hours later to have the test read. They will measure the size of any reaction (induration – a raised, hard area) in millimeters. The size of the reaction determines the interpretation. A positive reaction doesn't automatically mean you have active TB; further testing is needed.

Positive Result: A positive result suggests exposure to the TB bacteria. However, this exposure might have resulted in latent TB infection (LTBI), where the bacteria are present in the body but are not actively causing illness. Further testing is crucial to determine if you have LTBI or active TB.
Negative Result: A negative result suggests you haven't been exposed to the TB bacteria or that your immune system is not reacting to the tuberculin.
Indeterminate Result: Sometimes, the results are not clear-cut. This often happens due to an improper technique, not waiting the required 72 hours, or another underlying condition. Your doctor may need to repeat the test.

Who Needs a Mantoux Test?

The Centers for Disease Control and Prevention (CDC) recommends Mantoux testing for specific groups of people at higher risk of TB infection, including:

Healthcare workers: They have increased exposure to individuals with TB.
People with weakened immune systems: Those with HIV/AIDS or other conditions that suppress the immune system are at higher risk of developing active TB.
Recent immigrants from countries with high TB rates: Individuals from high-prevalence areas may have a higher chance of carrying the TB bacteria.
Close contacts of individuals with active TB: People living with or in close contact with someone diagnosed with active TB are at a greater risk of infection.
Residents and staff of long-term care facilities: These settings can provide an environment conducive to TB transmission.
Injection drug users: This group has an increased risk of contracting TB.

Limitations of the Mantoux Test

It's important to understand the limitations of the Mantoux test:

False positives: The test can sometimes give a positive result even if you don't have TB. This can occur due to previous BCG vaccination (used in many countries to prevent TB), other mycobacterial infections, or certain immune system conditions.
False negatives: The test may not always detect early TB infection, particularly in people with weakened immune systems.
Doesn't diagnose active TB: A positive Mantoux test only indicates exposure; it doesn't confirm active TB disease. Further tests like chest X-rays and sputum cultures are necessary to diagnose active TB.

What Happens After a Positive Mantoux Test?

A positive Mantoux test does not mean you have active TB. It requires further evaluation to determine if you have latent TB infection (LTBI) or active TB disease. Your doctor will likely order:

Chest X-ray: To visualize the lungs and look for any abnormalities consistent with TB.
Sputum culture: This test involves collecting a sample of sputum (mucus coughed up from the lungs) and analyzing it to detect the presence of TB bacteria.

If you are diagnosed with LTBI, treatment with antibiotics is generally recommended to prevent the infection from progressing to active TB. Active TB requires more extensive and longer-term antibiotic therapy.

Frequently Asked Questions about the Mantoux Test

Q: Is the Mantoux test painful?

A: The injection is typically only mildly uncomfortable, similar to a small pinprick.

Q: How long does it take to get the Mantoux test results?

A: You'll need to return 48-72 hours after the injection for the test to be read.

Q: What if I've had the BCG vaccine?

A: The BCG vaccine can cause a positive Mantoux test result, making interpretation more complex. Your doctor will consider this when interpreting your results.

Q: How much does a Mantoux test cost?

A: The cost varies depending on location and insurance coverage. It is generally a relatively inexpensive test.

The Mantoux test is a valuable tool in identifying individuals who may have been exposed to TB. However, it's crucial to remember that a positive result requires further evaluation to determine the next course of action. Always consult with a healthcare professional for diagnosis and treatment. Early detection and appropriate management are key to preventing the progression of TB.