Tuberculosis: Tests and Diagnosis

February 28, 2021 by ChestMed Pte Ltd.0
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In essence, tuberculosis or TB is a contagious infection that typically attacks the lungs. The infection can also spread to other parts of the body like the spine and the brain. Tuberculosis is caused by a bacteria known as Mycobacterium tuberculosis. In the 20th century, TB was considered the leading cause of death in the United States.

The great thing is tuberculosis treatment often only involves antibiotics and is actually straightforward. However, the treatment process can take a long time. Typically, you will be asked to take the medications for at least 6 to 9 months.

Tuberculosis Types

Having a TB infection will not always mean you will get sick. There are two types of tuberculosis:

Active TB: The germs can multiply and make you ill. When you have active TB affecting your lungs, you can spread the disease to others. At least 90 percent of active cases in adults started from a latent TB infection.

Latent TB: When you have latent TB, it means you have the germs in your body but your immune system is strong enough to keep it from spreading. You will not manifest any symptoms and you will not be contagious. However, you still have the infection and it can get active anytime. 

You have a higher risk of developing active TB if you have HIV, your chest X-ray is unusual, or your immune system is compromised. Your doctor will give you preventive tuberculosis treatment to ensure your latent TB infection will not become active. 

Tuberculosis Tests and Diagnosis

There are two kinds of tests that are used to detect the presence of TB bacteria in the body. There’s the TB blood test and the TB skin test (TST). A positive TB blood or skin test indicates that the individual has been infected with the TB bacteria. 

However, it won’t determine if they have latent TB infection (LTBI) or if it has progressed to active TB. Other tests like sputum sample and chest X-ray are needed to determine if someone has active TB. 

TB Skin Test

Also called the Mantoux tuberculin skin test (TST), this test will require two visits to your healthcare provider. On the first visit, the test is placed. Your healthcare provider will read the test on your second visit. 

  • The TB skin test is carried out by injecting a small amount of tuberculin into the skin found on the lower part of the arm.
  • Once given the tuberculin skin test, you need to return within 48 to 72 hours to have the healthcare provider check the reaction on your arm. 
  • The results will be based on the size of the swelling or the raised hard area.

Positive skin test: This means the body is infected with the TB bacteria. However, additional tests will be needed to check if the person has TB disease or latent TB infection.

When needed, a TB skin test can be repeated. If repeated, the additional test is done on another part of the body (i.e., the other arm, etc.). The TB skin test is often the preferred test for children that are under five years old.

TB Blood Test

An IGRA (Interferon Gamma Release Assay) is a blood test that is carried out to determine if a person has been infected with the TB bacteria. An IGRA will measure how strong the person’s immune system will react to the TB bacteria by testing their blood in a laboratory.

Positive IGRA: This means the person is infected with the TB bacteria. Additional tests will be needed to check if the person has latent TB infection only or active TB disease. 

Negative IGRA: This means the person’s blood did not react to the test and that both latent or active TB disease is unlikely.

ChestMed Pte Ltd.

ChestMed Pte Ltd.


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