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Testing for Tuberculosis - All You Need To Know

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Testing for tuberculosis can be done using blood and a skin diagnostic test. Read the article to learn more.

Medically reviewed by

Dr. Kaushal Bhavsar

Published At March 10, 2023
Reviewed AtMarch 10, 2023


Tuberculosis is a serious bacterial illness that primarily affects the lungs; although not always, it may attack the kidney, spine, and brain. It is caused by Mycobacterium tuberculosis and is not always easy to diagnose. Tuberculosis was a leading cause of death in the United States in the 20th century. However, most cases are cured today with antibiotics.

What Are the Different Types of Tuberculosis?

Tuberculosis bacteria can affect any part of the body, typically the lungs, spine, and brain. Tuberculosis can be classified into active and latent tuberculosis based on the appearance of symptoms. When the tuberculous bacteria affects the lungs, it is referred to as pulmonary tuberculosis; when it affects outside the lungs, it is referred to as extrapulmonary tuberculosis.

1. Active Tuberculosis: This is the contagious form of tuberculosis; it is also known as tuberculosis disease. The active form can be life-threatening if not treated properly. They show symptoms, although symptoms would depend on whether the infection is pulmonary or extra-pulmonary. The symptoms include:

  • Weight loss.

  • Fever.

  • Chills.

  • Fatigue.

  • Night sweats.

  • Loss of appetite.

2. Latent Tuberculosis: It is an inactive form of tuberculosis; in which the person does not experience any symptoms. The person will not be contagious but will show a positive test report. Approximately in 5 to 10 percent of people, the inactive form turns into the active form, predominantly in immunocompromised people due to medication or an underlying condition.

3. Pulmonary Tuberculosis: It is the active form of tuberculosis that affects the lungs. One may get the disease by inhaling contaminated air exhaled by a tuberculosis patient. The bacteria can remain in the air for hours. The symptoms include:

4. Extrapulmonary Tuberculosis: Tuberculosis that affects the rest of the body outside of the lungs, such as bones or organs. The symptoms of extrapulmonary tuberculosis depend on the part of the body affected.

5. Tuberculous Lymphadenitis: Affects the lymph nodes, especially the neck lymph nodes.

6. Skeletal Tuberculosis: Tuberculosis of the bone that spreads from the lungs or lymph nodes. It is a rare form of tuberculosis but is noticed at high rates among immunocompromised patients.

7. Miliary Tuberculosis: Spreads in the body, affecting one or multiple organs. It usually affects the bone marrow, lungs, and liver but may spread to the spinal cord, heart, and brain.

8. Genitourinary Tuberculosis: This affects the parts of the genitals and urinary tract, although kidneys are the most common sites. It may occur due to spreading from lymph nodes or lungs through the bloodstream or even through sexual intercourse.

9. Liver Tuberculosis: This affects the liver and is also known as hepatic tuberculosis.

10. Gastrointestinal Tuberculosis: Affects the gastrointestinal tract.

11. Tuberculous Meningitis: Tuberculosis that spreads to the meninges, from the lungs, or through the bloodstream.

12. Tuberculous Peritonitis: Tuberculosis causes the inflammation of the tissue layer covering the inside of the abdomen and its organs.

13. Tuberculous Pericarditis: Tuberculosis that spreads to the outer protective layer of the heart or the pericardium.

14. Cutaneous Tuberculosis: A rare form of tuberculosis that affects the skin.

What Are the Different Tuberculosis Tests?

Tuberculosis (TB) can be tested by two tests: TB skin test and TB blood test. The healthcare provider advises either of them depending on the reason for testing, cost, and test availability.

TB Skin Test: TB skin test or the Mantoux tuberculin skin test (TST) is a preferred TB test for children under five years. It involves two visits; on the first visit, the test is placed, and on the second visit, the reports are made. During the first visit, the healthcare provider injects a small amount of fluid (tuberculin) into the skin of the arm of the patient. The second visit is usually 48 to 72 hours after the first visit. On the second visit, the healthcare provider looks for a reaction on the arm.

  • Positive Skin Test: A positive skin test indicates that the person is infected with tuberculous bacteria. Confirmatory tests are required to determine if the person has a latent TB infection or disease.

  • Negative Skin Test: A negative skin test indicates that the person did not react to the test and may not have the infection.

The healthcare provider may repeat the tests. However, the tests may sometimes show a false positive reaction if one has taken the BCG (bacillus Calmette–guérin) vaccine or has had the infection in the past.

  • TB Blood Test: It is also known as interferon-gamma release assay (IGRA). It measures the response of the immune system to TB antigens.

The healthcare provider will send the blood drawn from the patient to the lab for analysis.

  • Positive TB Blood Test: A positive blood test indicates that the person is infected with tuberculous bacteria.

  • Negative TB Blood Test: A negative blood test indicates that the person did not react to the test and may not have the infection.

TB blood tests are preferred in people who have taken the BCG vaccine and in people for whom the second visit for a skin test would be difficult.

  • Other TB Tests: If the TB blood or skin test is positive, the healthcare provider would advise a chest X-ray and a sputum smear or culture test. The chest X-ray may show spots on the lungs if it is an active TB infection, and the culture may find the TB bacteria. However, in latent infection, both will be negative.


Tuberculosis is an illness that affects most often the lungs but may also affect other parts of the body, including the skin, the heart, the brain, and the kidneys. It is a severe illness and needs to be tested and treated appropriately. A healthcare provider must be consulted if one suspects symptoms of tuberculosis or is at high risk of the disease. The doctor may advise antibiotics for at least six to nine months, and it is vital to take the course of medication to recover from the condition completely.

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Dr. Kaushal Bhavsar
Dr. Kaushal Bhavsar

Pulmonology (Asthma Doctors)


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