Mantoux Test - Purpose, Procedure, Results Interpretation, Normal Values and more

The Mantoux test, also known as the tuberculin skin test (TST), is a diagnostic procedure used to determine if a person has been exposed to Mycobacterium tuberculosis, the bacterium responsible for causing tuberculosis (TB). TB remains one of the most significant infectious diseases worldwide, with millions of new cases each year. Early detection of TB is crucial for treatment and preventing its spread to others.

The Mantoux test involves injecting a small amount of purified protein derivative (PPD), a substance derived from the TB bacterium, just beneath the skin. The test helps identify individuals who may have been exposed to TB and are at risk of developing the disease. While not a definitive diagnosis for active TB, the Mantoux test plays a critical role in screening for latent tuberculosis and identifying individuals who may need further testing.

What is the Mantoux Test?

The Mantoux test is a skin test used to detect latent tuberculosis (TB) infection. The test involves injecting a small amount of PPD (a protein derivative from the Mycobacterium tuberculosis bacterium) just under the surface of the skin, usually on the inner forearm. After 48 to 72 hours, the test site is examined to see if there is a reaction. The size of the raised, red area at the injection site is measured, which helps determine whether a person has been exposed to TB.

How the Mantoux Test Works

1. Injection of PPD: The healthcare provider injects a small amount of PPD just under the skin, typically on the inner forearm.
2. Observation Period: The test site is left undisturbed for 48 to 72 hours to allow the body to respond to the PPD. It’s important that the test site is not scratched or rubbed during this time.
3. Test Reading: After the observation period, a healthcare provider will measure the size of the raised, red area (induration) at the injection site. The diameter of the induration is measured in millimeters (mm), which helps determine the test result.
4. Interpretation: The results are interpreted based on the size of the induration, the patient’s medical history, and risk factors for TB exposure.

Why is the Mantoux Test Performed?

The Mantoux test is primarily used for screening and detecting latent tuberculosis infection. While it does not definitively diagnose active TB, it helps identify individuals who may have been exposed to the Mycobacterium tuberculosis bacterium and are at risk of developing active TB in the future.

1. Screening for Latent Tuberculosis

The Mantoux test is used to screen individuals who may have been exposed to TB but do not show symptoms of the disease. Latent tuberculosis means that the person has been infected with Mycobacterium tuberculosis but does not have active symptoms. It is important to identify latent TB as it can develop into active TB if left untreated.

2. Identifying High-Risk Individuals

Individuals who are at higher risk for TB exposure are commonly tested with the Mantoux test. High-risk groups include:

• People living with individuals who have active TB
• Individuals with weakened immune systems, such as those with HIV/AIDS
• Healthcare workers who are in frequent contact with TB patients
• People who have traveled to regions where TB is endemic

3. Assessing Newborns and Children

Children under the age of 5 and infants in areas where TB is prevalent are often tested with the Mantoux test as part of routine healthcare screening.

4. Pre-employment or Immigration Requirements

Certain immigration policies or employment screenings may require a Mantoux test to ensure individuals are not carrying the TB bacterium and to prevent the spread of TB in public spaces like schools or healthcare facilities.

5. Monitoring TB Treatment

For individuals undergoing treatment for latent TB, a Mantoux test may be repeated to evaluate the effectiveness of the treatment.

How to Prepare for the Mantoux Test

Preparing for the Mantoux test is straightforward, as it is a non-invasive procedure that does not require fasting or significant preparation. However, there are a few important things to keep in mind:

• Inform Your Healthcare Provider: Inform your healthcare provider if you have had a prior positive TB test or if you have a history of allergies to any medications or substances, as this may affect the test results.
• Avoid Scratching or Rubbing the Injection Site: After receiving the test, it is important not to scratch, rub, or apply any creams to the injection site, as this can affect the results. Keep the area clean and dry.
• Avoid Exposure to Strong Irritants: Avoid strong perfumes or chemicals that may irritate the skin at the injection site.
• Inform About Any Vaccinations: If you have received any recent vaccinations, particularly BCG vaccine, let your healthcare provider know. The BCG vaccine can affect the Mantoux test result, leading to a false positive result.
• Medications: Inform your healthcare provider if you are on any medications, especially if they affect your immune system. Some treatments may alter your body’s response to the test.

Test Results Interpretation

The Mantoux test result is interpreted based on the size of the induration (the raised bump or hard area that appears at the injection site) measured in millimeters (mm). The size of the induration varies based on several factors, including the individual’s risk level, their immune status, and the history of TB exposure.

1. Negative Result

No induration or a very small amount (less than 5mm) at the test site indicates a negative result, meaning the person has not been infected with the TB bacterium.

2. Positive Result

The result is considered positive when the induration is greater than 5mm. However, the size of the induration is interpreted differently depending on the person’s risk factors:

• 5mm or greater: Typically positive for individuals with a weakened immune system, healthcare workers, or those who have had close contact with someone with active TB.
• 10mm or greater: Positive for individuals with moderate TB risk, including those who live in endemic areas or have recently traveled to high-risk countries.
• 15mm or greater: Positive for individuals with no known risk factors but are showing signs of possible latent TB exposure.

3. False Positive Results

A false positive result can occur in individuals who have previously received the BCG vaccine (which protects against TB but can cause a mild reaction to the Mantoux test). In these cases, the test result may be incorrectly interpreted as positive.

4. False Negative Results

A false negative result can happen if the immune system is too weak to react to the PPD, as may occur in people with HIV/AIDS or those on immunosuppressive medications. It can also occur in individuals who have been exposed to TB for a long time but have not developed a strong immune response yet.

10 Frequently Asked Questions About the Mantoux Test

• What is the Mantoux test? The Mantoux test is a skin test that checks for latent tuberculosis (TB) infection by injecting a small amount of purified protein derivative (PPD) from the TB bacterium under the skin.
• Why do I need a Mantoux test? The test is used to determine if you’ve been exposed to the tuberculosis bacteria and to assess your risk of developing active TB. It’s commonly done as part of a screening process for high-risk individuals.
• How is the Mantoux test performed? A small amount of PPD is injected under the skin, and the injection site is checked 48 to 72 hours later to measure any redness or swelling (induration).
• What do the results of the Mantoux test mean? The results are interpreted based on the size of the raised area. A larger area of induration suggests that the person has been exposed to TB, while a smaller or no induration suggests no exposure.
• Does the Mantoux test hurt? The Mantoux test involves a small needle injection into the skin. You may experience mild discomfort or a slight sting during the injection, but it is generally not painful.
• What happens if I test positive for the Mantoux test? A positive result does not necessarily mean you have active TB. It indicates latent tuberculosis, and further tests (such as a chest X-ray or sputum test) may be needed to determine if the infection is active.
• Can a false positive occur with the Mantoux test? Yes, a false positive can occur, particularly in individuals who have received the BCG vaccine. Other factors like prior exposure to non-tuberculosis mycobacteria can also cause a false positive.
• What if I test negative for the Mantoux test? A negative result typically means you have not been exposed to TB. However, if you have symptoms or a history of TB exposure, further testing may be needed.
• Is the Mantoux test safe? Yes, the Mantoux test is safe and non-invasive, though you should avoid scratching the test site to ensure accurate results.
• Can I get a Mantoux test if I’m pregnant? Pregnant women can undergo a Mantoux test, as it poses no known risks to the pregnancy. However, your doctor may advise additional precautions or monitoring.

Conclusion

The Mantoux test is a vital tool in screening for latent tuberculosis (TB) infection. Although it cannot diagnose active TB, it helps identify individuals at risk and provides the first step in the process of TB diagnosis. Timely detection and treatment of latent TB are essential to prevent the development of active tuberculosis and to stop its spread.

Whether you’re undergoing a routine screening or are being tested due to suspected exposure, understanding the Mantoux test, its uses, and how to interpret the results will help you navigate the process with confidence. If you have concerns or questions about the test, always consult with your healthcare provider for personalized guidance. Early diagnosis and treatment are key to managing TB and ensuring the health of individuals and the community.