Understanding the Mantoux Test: Procedure, Results, and Interpretation
Time to read 8 min
Time to read 8 min
TB, or tuberculosis, is one of the most infectious diseases worldwide. Around one million new cases are reported every year. Timely detection of tuberculosis is crucial for effective treatment and preventing the infection from spreading to others. The Mantoux Test, also known as the Tuberculin skin test (TST), is performed to diagnose tuberculosis (TB).
The diagnostic procedure determines if a person is exposed to Mycobacterium tuberculosis, which causes tuberculosis. While this test is not a definitive diagnosis of active TB, the test has a significant role in the screening of latent TB. The test helps identify people who may necessitate further testing.
The Mantoux test is a skin test that is conducted to spot tuberculosis infection. The test helps diagnose if you have even been exposed to M. tuberculosis complex. However, the TB skin test may not distinguish between a latent and an active TB infection. You may need additional tests, such as a sputum test, to check if you have an active infection.
TB skin tests are more common and are most prescribed for children under 5 years of age. A small amount of the protein derived from Mycobacterium tuberculosis bacterium (PPD) is injected right under the skin, generally on the inner side of the forearm. The site should not be rubbed or scratched during this period.
The test site is investigated after 48 to 72 hours to check if there is a reaction. The size and the redness of the raised skin (induration) are measured to determine if the individual has been infected with TB bacterium. The diameter of the induration is measured to conclude the results. The test results are interpreted based on size, risk factors for TB exposure, and medical history.
Typically, the Mantoux test is used for screening and diagnosing latent tuberculosis infection. Although it is not an ultimate diagnosis of active TB infection, it helps determine if the person has been exposed to mycobacterium tuberculosis and if the person is at risk of developing TB in the future.
The Mantoux test is performed to identify individuals who have been exposed to TB bacterium but are not having any active symptoms. Latent tuberculosis means the person has been infected with TB but does not have active symptoms. It is important to detect latent TB infection as it can lead to active TB if not treated or managed well.
Usually, the Mantoux test is recommended for people carrying a higher risk of acquiring TB. High-risk people include people living with patients who have an active TB infection, people with weakened immune systems, healthcare workers having frequent contact with TB Patients, and individuals who have visited TB-prone regions where TB is endemic.
Infants and children below 5 years who are born or living in regions where TB is prevalent are usually tested. These children are prone to getting the infection, so they are often tested with the Mantoux test as a part of routine healthcare screening.
Certain employment screenings and immigration policies may necessitate a Mantoux test to make sure individuals are free of TB bacteria and also to prevent the spread of diseases in public spaces.
Mantoux test may be repeated in patients who are taking treatment for latent TB. It helps evaluate the efficacy of the ongoing treatment.
You should get tested if you are experiencing symptoms of an active TB infection or if you are at greater risk of developing TB. Additionally, some hospitals, child care centers, and certain facilities prefer testing before you join them.
Get tested for TB if you:
The test results depend on the response of the injection on the skin. The reaction should be examined by the medical professional within 48 to 72 hours of injection. The bump formed on the skin needs to be measured in millimeters, excluding the surrounding redness. The lump should be measured across the forearm.
The analysis of the Mantoux test result depends on various factors, including:
A very small amount or no induration signifies a negative result, which means the person has not developed the TB bacterium.
If the size of the induration is greater than 5mm, it means the Mantoux test is positive. However, the precise measurement is evaluated depending on the risk factors.
A false positive result may happen in people who have previously received the BCG vaccine. The test result may be incorrectly interpreted as positive in such cases.
A false negative Mantoux test result may be if the immune system is too weak to respond to the PPD. It may occur in individuals with HIV infection or who are taking immunosuppressive medicines. It can also occur in individuals who have been infected with TB for a long time but have not developed a significant immune response yet.
Factors affecting the interpretation of results include age, medical history, risk of TB exposure, current immune status, previous BCG vaccination, and size of the induration.
The positive test result appears as a red, firm bump on the test site. The healthcare professional will measure the size of the firmness of the bump. The healthcare provider considers your particular risk factors to evaluate the test results for you.
A positive Mantoux test indicates that you have been exposed to the tuberculosis bacterium. In this case, your doctor or healthcare provider will order further tests to make a precise diagnosis. The tests that detect active TB infection include laboratory tests on a sputum sample and chest X-rays. Sputum is a different type of saliva, thick mucus that you cough up from the lungs. Whether it is diagnosed as latent or active TB, you necessitate treatment.
The positive TB skin test result signifies that the person has been exposed to TB bacteria, but it does not mean that it is an active TB. If there are no symptoms of TB, it indicates that currently, the person is not at risk of spreading the bacteria to others, but they may acquire the disease in the future. The decision concerning the latent TB treatment should be made by the healthcare provider who can assess the risk factors of developing an active TB infection.
A negative test result signifies that you are not infected with the TB bacterium. When the test is negative, your skin does not react to the liquid that is injected at the test site. In case you are experiencing the symptoms of TB but your test results are negative, your doctor may order further testing.
Yes, TB can be present even if the Mantoux test is negative. It may happen due to various reasons, such as:
If you were infected with TB for the last 8 weeks, your immune system may not have had sufficient time to create a detectable response.
Patients with advanced immunosuppression or untreated HIV may have false-negative results on the Mantoux test.
In case the blood sample is not collected properly, handled incorrectly, or an assay is performed inappropriately, the test results can be false negative.
Some individuals with inactive TB may have negative skin test results, however, they may have a positive result if tested again within a year.
If you have visible symptoms of TB, including chest pain, coughing, fever, tiredness, and weight loss, seek medical advice from your healthcare provider. Other TB tests include sputum samples, urine sample tissue samples, and chest radiographs.
Negative Mantoux test results indicate that the person has not been exposed to TB bacteria however, a false negative can happen due to various factors such as a recent TB infection, recent live virus vaccination, a weakened immune system, malnutrition, and certain medications (corticosteroids).
The Mantoux test is a significant tool in detecting latent tuberculosis infection. Although it may not detect an active TB infection, it helps recognize individuals at higher risk and acts as the first step in the TB diagnosis process.
If you have any concerns regarding the test, consult your doctor for personalized guidance. Early diagnosis and the right treatment are crucial to managing TB and ensuring individuals' health. TB testing and diagnosis are vital for public health. Since TB can be fatal and spreads easily, it's essential to get tested if your symptoms put you at higher risk of developing active TB or at high risk of being exposed to infection. Don’t hesitate to ask any questions.
A small amount of PPD is injected under the skin on the inner side of the forearm. Then, the injection site is assessed after 48-72 hours, and the bump and redness (induration) are measured.
The Mantoux test results are interpreted depending on the size of the raised area at the test site. The larger area of induration means the person is exposed to TB, while a smaller or no induration signifies no exposure.
The Mantoux test involves injecting PPD into the skin. A small needle is used during the process. You may experience a slight sting or mild discomfort but it's not painful.
Yes, some patients may experience fever after the Mantoux test. However, these kinds of side effects are uncommon. The fever is normal and can be managed with medication under the direction and supervision of a healthcare professional.
Positive or negative results of the Mantoux test may indicate the presence or absence of TB bacteria, whether in latent or active form. Further tests may be advised to diagnose tuberculosis.
***Medical Disclaimer: The following information is for educational purposes only. No information provided on this website, including text, graphic, and images, is intended as substitutes for professional medical advice. Please consult your healthcare provider for medical advice concerning your particular medical condition(s).
