The Mantoux test, also known as the tuberculin sensitivity test, is a diagnostic tool used to determine if a person has been exposed to the bacterium that causes tuberculosis (TB). During the test, a small amount of purified protein derivative (PPD) is injected under the skin's surface. The injection site is then observed for any signs of a reaction, such as redness, swelling, or hardening of the skin, which can indicate exposure to the TB bacteria.

What is a Mantoux / Tuberculin Sensitivity Test? 

The Mantoux test, also known as the tuberculin sensitivity test, is a diagnostic tool used to determine if a person has been exposed to the bacterium that causes tuberculosis (TB). During the test, a small amount of purified protein derivative (PPD) is injected under the skin's surface. The injection site is then observed for any signs of a reaction, such as redness, swelling, or hardening of the skin, which can indicate exposure to the TB bacteria. 

While the Mantoux test can indicate if a person has been exposed to TB, it cannot confirm if the person has an active TB infection. 

What is the purpose of a Mantoux / Tuberculin Sensitivity Test? 

The Mantoux test is used to detect whether a person has been exposed to the bacterium that causes tuberculosis (TB). This test is commonly used as a screening tool to identify individuals who may have TB or have been in contact with someone with the disease. It is also used to screen healthcare workers and people who work in close quarters with others, as they may be at an increased risk of contracting TB. If the Mantoux test result is positive, further testing, such as a chest X-ray or sputum test, may be necessary to confirm the presence of active TB. Early detection of TB is important, as it allows for prompt treatment and can prevent the spread of the disease to others.

What does the Mantoux / Tuberculin Sensitivity Test diagnose? 

The Mantoux test, also known as the tuberculin sensitivity test, diagnoses the following: 

• Exposure to the bacterium that causes tuberculosis (TB) 
• Latent tuberculosis infection (LTBI)  

The test does not diagnose: 

• Active TB disease 
• Previous vaccination against TB  

A positive test result indicates exposure to the TB bacterium and the need for further testing to determine if the individual has LTBI or active TB disease. 

Preparation and procedure required for a Mantoux / Tuberculin Sensitivity Test 

Preparation for the Mantoux/Tuberculin Sensitivity Test: 

• You should inform the healthcare provider if you have any allergies or medical conditions that may affect the test result. 
• You should also inform your healthcare provider if you have received the BCG vaccine, as this can affect the test result. 
• The healthcare provider will check if you have any skin conditions that may interfere with the test, such as eczema or psoriasis.  

Procedure for Mantoux/Tuberculin Sensitivity Test: 

• The healthcare provider will clean the injection site with an alcohol swab. 
• Using a small needle, the healthcare provider will inject a small amount of purified protein derivative (PPD) under the skin on the forearm. 
• The healthcare provider will record the date, time, and amount of PPD injected. 
• The person should avoid rubbing or scratching the injection site. 
• Visit the healthcare provider after 48-72 hours (about 3 days) to check the injection site for a reaction. 
• The healthcare provider will check any redness, swelling, or hardening of the skin at the injection site and record the results. 

After the test  

After the Mantoux/Tuberculin Sensitivity Test, you should follow these steps: 

• Avoid touching, rubbing, or scratching the injection site to prevent irritation. 
• Do not cover or bandage the injection site. 
• Avoid exposing the injection site to water for at least 48-72 hours (about 3 days) after the test, as water can affect the result. 
• Observe the injection site for any signs of reaction, such as redness, swelling, or skin hardening. 
• Inform the healthcare provider if there is redness, swelling, or pain at the injection site.  

Understanding the Mantoux / Tuberculin Sensitivity Test Results 

The interpretation of the Mantoux/Tuberculin Sensitivity Test results will depend on several factors, including the size of the induration (hardening of the skin) at the injection site, the person's medical history, and the prevalence of TB in the community. 

A positive test result indicates that you have been infected with the bacterium that causes TB, but it does not necessarily mean you have active TB disease. A negative test result indicates that a person has not been infected with TB, but a negative test result is not always conclusive, as some people may have false-negative results, especially if they have compromised immune systems. 

To interpret the results of a Mantoux test, healthcare providers use a specific measurement called the "induration" size, which refers to the size of the hardened area around the injection site. The size of the induration is measured in millimetres (mm) and is used to determine whether the test result is positive, negative, or uncertain. 

In general, the interpretation of a Mantoux test result is as follows: 

• Negative result: A negative result means that no reaction was observed at the injection site within 48-72 hours (about 3 days). This usually means that the person has not been infected with TB, but it is important to note that a negative result does not always rule out TB infection. 
• Positive result: A positive result means that a reaction was observed at the injection site within 48-72 hours (about 3 days). The size of the reaction is measured in millimetres of induration (swelling), and a larger induration usually indicates a stronger reaction. 
• A reaction of 5mm (about 0.2 in) or more is considered positive for HIV-positive people, recent contacts of TB cases, or chest X-ray findings suggestive of TB. 
• A reaction of 10mm (about 0.39 in) or more is considered positive for people who have travelled from high-prevalence countries, are drug users, have medical conditions that increase the risk of TB, or work or live in high-risk settings such as healthcare facilities, correctional institutions, or homeless shelters. 
• A reaction of 15mm (about 0.59 in) or more is considered positive for people who have no known risk factors for TB. 
• False-positive result: A false-positive result can occur in people vaccinated with the BCG vaccine or exposed to nontuberculous mycobacteria.  
• False-negative result: A false-negative result can occur in people who have compromised immune systems, such as people living with HIV or people who have received immunosuppressive therapy. These people may have TB infection, but the test result can still be negative. ​​​​​​​

Depending on the results of the Mantoux/Tuberculin Sensitivity Test, the following steps may be taken: 

Negative test result: 

• If the test result is negative, it means that the person has not been infected with the TB bacterium. No further testing or treatment is required unless there has been recent exposure to TB or other risk factors are present. 

Positive test result:

• If the test result is positive, it means that the person has been infected with the TB bacterium, but it does not necessarily mean that they have active TB disease. Further testing is required to determine if the person has latent TB infection or active TB disease. The healthcare provider may recommend a chest X-ray and/or sputum test to determine if the person has active TB disease. If the person has a latent TB infection, the healthcare provider may recommend treatment to prevent the infection from progressing to active TB disease. If the person has active TB disease, they will need to undergo treatment with antibiotics to cure the infection and prevent the spread of TB to others.  

Uncertain test result: 

• In some cases, the Mantoux test result may be uncertain or difficult to interpret, such as if there is significant swelling or redness at the injection site. 

• In these cases, the healthcare provider may recommend repeating the test or performing additional testing, such as a blood test or a different type of skin test, to confirm the result.