what is mantoux testing

4 min read 31-12-2024

Meta Description: Mantoux testing, also known as the tuberculin skin test (TST), is a simple and effective way to screen for tuberculosis (TB) infection. Learn about the procedure, results, and limitations of this important test in our comprehensive guide. Discover how it works, what to expect, and when you might need it. This guide clarifies the process and helps you understand its significance in TB detection.

What is the Mantoux Test?

The Mantoux test, also known as the tuberculin skin test (TST) or PPD (purified protein derivative) test, is a common screening tool used to detect infection with Mycobacterium tuberculosis, the bacteria that cause tuberculosis (TB). It doesn't directly detect active TB disease, but rather identifies whether you've been exposed to the bacteria and developed an immune response. This is crucial because latent TB infection can reactivate later in life.

How Does the Mantoux Test Work?

A small amount of tuberculin, a purified protein derivative from the TB bacteria, is injected just under the skin of your forearm. This injection creates a small wheal (a raised bump). You'll return 48-72 hours later for a healthcare professional to measure the size of any reaction.

Reading the Mantoux Test Results

The test is read by measuring the diameter of any induration (hardening or swelling) at the injection site, not redness. A healthcare professional will measure the reaction in millimeters. The interpretation of the results depends on several factors including:

Your risk factors for TB: People with a higher risk (e.g., those living in areas with high TB prevalence, individuals with weakened immune systems, or recent close contact with someone who has TB) may be diagnosed with latent TB infection even with smaller reactions.
Your overall health: Pre-existing health conditions can affect the test's accuracy.

The results are generally interpreted as follows:

Negative: A reaction less than 5mm is usually considered negative in most individuals. However, those at high risk might require further investigation, even with a negative result.
Indeterminate: A reaction between 5mm and 10mm is considered indeterminate, meaning further evaluation is needed based on individual risk factors.
Positive: A reaction of 10mm or more is usually considered positive, suggesting exposure to TB bacteria. This does not automatically mean you have active TB. Further testing is needed to determine if the infection is latent or active.

Important Note: A positive Mantoux test doesn't always mean you have active TB. It simply indicates that you've been exposed to the bacteria and your immune system has reacted. Further tests, such as a chest X-ray and sputum culture, are needed to confirm if the infection is active.

Who Needs a Mantoux Test?

The Mantoux test is recommended for specific groups of people, including:

Healthcare workers: They are at increased risk of exposure to TB.
People with weakened immune systems: Their risk of developing active TB is higher.
Individuals with recent contact with someone who has TB: This is crucial for early detection and prevention.
Immigrants and refugees from countries with high TB prevalence: Screening helps identify cases early.
Residents and employees of long-term care facilities: These settings can facilitate TB transmission.
Individuals with certain medical conditions: Certain conditions increase the risk of TB reactivation.

What to Expect During the Mantoux Test

The Mantoux test is a quick and relatively painless procedure. Here's what to expect:

Injection: A small amount of tuberculin is injected just under your skin. You might feel a slight prick.
Waiting period: You'll need to return 48-72 hours later for the healthcare professional to read the test.
Reading: The healthcare professional measures the diameter of any induration (hardness) at the injection site.
Results: You'll receive your test results, and further investigations may be recommended depending on the result and your risk factors.

Limitations of the Mantoux Test

While the Mantoux test is a valuable tool, it's important to be aware of its limitations:

False-positive results: Factors like prior BCG vaccination (a vaccine against TB) can cause false-positive results.
False-negative results: People with weakened immune systems may have a negative test even if they have a TB infection.
Does not detect active TB: It only detects exposure to the bacteria. Further testing is necessary to diagnose active TB disease.

Frequently Asked Questions about Mantoux Testing

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

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

Q: Is the Mantoux test painful?

A: The injection is usually only mildly uncomfortable, like a small pinprick.

Q: What should I do if I have a positive Mantoux test result?

A: A positive result indicates exposure to TB bacteria, not necessarily active disease. Further testing, including chest X-rays and sputum cultures, is crucial to determine if you have latent TB infection or active TB disease. Your doctor will advise on appropriate follow-up care.

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

A: The BCG vaccine can interfere with the results of the Mantoux test, potentially leading to a false-positive result. Your doctor will take this into account when interpreting your results. They may also use different criteria for interpreting the result.

This comprehensive guide provides a detailed understanding of Mantoux testing. Remember, this information is for educational purposes only, and should not be considered medical advice. Always consult with a healthcare professional for any health concerns or before making any decisions related to your health or treatment.