TB is short for Mycobacterium tuberculosis, or tuberculosis. It’s a type of bacteria attacks the lungs, but it can affect any part of the body, like the kidneys, the spine, or the brain.
India continues to share the highest global burden of the disease with a number of interventions in place for screening the patients and providing them with treatment.
Many people who have TB don’t show any symptoms. This is called as latent TB. However, a TB skin test is usually the first method the doctors use to diagnose TB.
Procedure for TB skin test
The TB skin test has two parts. The first part involves the doctor injecting the patient with a small amount of a sterile solution, containing tuberculin. Tuberculin is a fraction of purified protein derived from Mycobacterium tuberculosis. If the patient has TB, their immune system will react to the tuberculin given in the TB skin test. The injection is usually done on the inside of the forearm. When it is done correctly, the injection will create a small, pale-colored bump on the skin called a wheal.
The second stage takes place between 49-72 hours after the first step is complete. The doctor will check how the tuberculin has reacted to the body. If you miss this appointment, you will have to do the whole process from the beginning again.
Understanding the results
The first thing the doctor tries to understand is the size of the lump on the arm where tuberculin was given. Bump smaller than five millimeters (mm) means result is negative. Bump larger than five mm means result is in the positive range.
If the bump is larger than five mm, the doctor will conduct further investigations to understand the factors involved in the TB. Few of them are mentioned below:
- Recent contact with another person with TB
- Working at a medical facility, such as a hospital, care center, or medical lab
- History of TB
- Receiving an organ transplant
- Taking immunosuppressant drugs
- Being HIV positive
- Recent visit to a country where TB is very common
- Using injected drugs
Sometimes, there is room for error in TB skin tests. Results may also come out to be false positive or false negative when not conducted correctly. If the diagnosis is unclear, doctors may conduct further tests to come to the right conclusion.