Mantoux Test

Doctors order Mantoux test in the following cases:

• When a person has been showing unexplained weight loss, cough and night sweats
• When a person has an abnormality in the chest X-ray
• When a person has been in close contact with someone affected with TB
• When a person has undergone a recent transplant surgery or has been tested positive for HIV infection
• For healthcare professionals who are always surrounded by people affected with TB

There are many situations where a Mantoux test is not recommended to be performed. Therefore, it is important to inform the doctor if you have had a severe reaction to this test in the past. Mantoux test is not advised if a person is already diagnosed with TB. 

Also, make sure to inform your doctor if you have been immunised with BCG vaccine or if you already have a skin rash from some other condition since it could lead to a false-positive result. 

Lastly, tell the doctor if you are taking any medicines or supplement. Do not change the course of any medication unless recommended by the doctor.

(Health checkup app)

A very small amount of tuberculin containing fluid will be injected on your left hand right beneath the skin. A nurse will clean and sanitise the injection site before injecting the fluid.

The injection will make a small bump on the skin (called a wheal), approximately 6 to 10 mm in diameter. Some technicians mark the bump on the skin with a pen. The area is left uncovered, and you are supposed to see your doctor after 48 to 72 hours for interpretation of results.

The test will not take very long, but there are a few risks involved. There could be a severe allergic reaction from the bump, such as fever or swelling of the arm or armpits. If this is the case, one must inform the doctor immediately. Since there are no live bacteria in the testing solution, there is no chance of acquiring TB due to the solution.

Normal results:
The results of this test are given in terms of length (millimetres) of the swelling on the arm where the testing solution has been injected. The characteristics of the bump are also taken into consideration for understanding the result.
If the area of injection is only red and the size is less than 5 mm, without any other symptoms, it means that the person is probably not affected by TB, which is a negative result. Also, there are chances of false-negatives with this test, which would mean that the person is infected with TB, but the result shows otherwise as in the following cases:

• Presence of viral infection, such as measles or chickenpox
• Presence of a severe unknown TB infection
• Weakened immune system, which is unable to show a reaction
• Presence of an extremely old TB infection
• Person tested is very young (less than 6 months old)
• Recent vaccination to viral infections

Abnormal results:
If results show up to be abnormal or positive, there is a major probability that the person is infected with TB or may show symptoms soon. The size of the bump and its characteristics have a direct correlation with this likelihood. The following list shows the relationship between the size of the bump and the chances of infection in different groups of people:

• A 5-mm bump, which is also red and hardened: This kind of result is considered positive if the person is taking immunosuppressant medicines; has undergone transplant surgery; is infected with HIV; came in contact with anyone infected with TB or had consistent changes in chest X-ray
• A 10-mm bump, which is also red and hardened: This result is considered positive if the person lives or is employed in a highly crowded area; is a Mycobacterium laboratory personnel; had immigrated from a high-risk country or is a user of injectable drugs. Children and infants who have been exposed to people infected with TB and show this kind of reaction are also said to have a positive result
• A 15-mm bump, which is also red and hardened: This result is considered positive for people who were known to have no risk of TB infection 

The test has a high incidence of false positives as in the following cases:

• Previous immunisation with BCG vaccination
• If the person has another Mycobacterium infection
• The testing solution is not injected properly, a wrong testing solution is injected or the interpretation of the result is improper.

As it is clear that the results of Mantoux test are difficult to interpret, it is necessary to refer to a doctor to understand them. To confirm the results of Mantoux test, your doctor may order a few other tests.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.