Tuberculosis (TB) is a communicable disease infecting the lungs. It is spread through droplets present in a person’s sneeze, cough, and spit. A tuberculosis test is done to look for Mycobacterium tuberculosis, the bacteria responsible for causing this disease. Since tuberculosis is preventable as well as curable, proper diagnosis with a TB test along with other screenings is highly recommended.

Overview of the Tuberculosis Test

A tuberculosis test aims to identify whether an individual has contracted the tuberculosis-causing bacteria. There are two types of tuberculosis tests: the TB skin test and the blood test. They help identify latent or active TB infection. A healthcare professional will order these tests if tuberculosis is suspected, if the person has been exposed to someone with active TB, or if the person is at risk for the disease.

About Tuberculosis Test

A tuberculosis screening test checks if a person has the Mycobacterium tuberculosis complex—the bacteria which cause tuberculosis. Common methods include the tuberculosis skin test (Mantoux test) and the tuberculosis blood test (Interferon-Gamma Release Assay). These tests assist in determining if a person has a TB infection, but they are unable to differentiate between a latent and active TB infection. With a positive tuberculosis test, the person will need additional tests to determine the right treatment.

Why Doctors May Recommend Tuberculosis Test?

A healthcare provider may order a diagnostic test for tuberculosis if a person has symptoms of an active TB infection or if they are at a higher risk of getting it.

An individual has a higher risk of being exposed to TB germs when:

• Live, work, or travel to countries where TB is common, like some countries in Asia, Africa, and South America.
• Work in places where TB is likely to spread, such as hospitals, homeless shelters, and nursing homes.
• Have been exposed to someone with an active TB infection
• Live or used to live in communal settings where TB is common, such as homeless shelters, prisons, or jails.

A person may require a tuberculosis test if they have symptoms of active TB, such as:

• A cough that lasts longer than three weeks
• Coughing up blood or sputum
• Chest Pain
• Fatigue
• Loss of appetite
• Weight loss
• Night sweats

The factors that will increase the risk of developing active TB disease include:

• Having certain medical treatments or procedures, like organ transplants or starting immunosuppressive therapy.
• Have a weaker immune system because of certain medical conditions like diabetes, HIV, or cancer.
• Have been infected with the TB germ in the last two years.
• Young children, under five years of age.
• They were not treated properly for TB infection in the past.
• Have injected illegal drugs.

Preparations Before the Tuberculosis Test

There are no special preparations required for the tuberculosis (TB) test. It is simple and requires minimal effort. Here are a few steps and considerations to keep in mind:

• Inform your Healthcare Provider: Let your doctor know if you have had the Bacille Calmette-Guérin (BCG) vaccine or have any medical conditions.
• Share Medication List: It is advisable to share any medications you are taking with the doctor before the test.
• No Fasting Needed: For tuberculosis blood tests and skin tests, there is no need for fasting. Maintain overall health with proper nutrition before the test.
• Wear Comfortable Clothing: Both tuberculosis tests involve a small needle, so it is advisable to wear short sleeves or loose clothing to allow easy access to the forearm.
• Visit for Follow-Up: After the tuberculosis skin test, you will need to return to the clinic 48-72 hours later for the reading, so schedule your visit accordingly.

What to Expect During the Procedure?

The process of a TB test is different based on what kind of test is prescribed by the doctor—a TB blood work test or a skin test.

 TB Skin Test Process

• During the TB skin test, a healthcare provider will clean and disinfect the area on your inner forearm.
• They will inject a small amount of tuberculin or PPD under the skin of your forearm.
• The doctor may mark the injection site by circling the area with a pen.
• Healthcare providers will ask you to return after 48 to 72 hours to look for the reaction on your forearm.
• A firm swelling or redness at the site may indicate a TB infection.

 TB Blood Test Process

• A phlebotomist will disinfect the inner part of the arm and insert a small needle in the vein to take a blood sample.
• A small amount of blood will be collected in a test tube.
• They will remove the needle, hold a cotton ball on the site to stop bleeding and place a bandage.
• The blood sample will be sent to the laboratory for testing, and your healthcare provider will share the results.

Understanding the Test Results

The tuberculosis test results vary depending on the type of test performed. However, these tests only show if you have been exposed to the tuberculosis infection, not if the infection is active or inactive.

Positive TB Test  

Tuberculin Skin Test

After administering the tuberculin skin test, a healthcare provider will check the injection site after 48 to 72 hours. The positive TB skin test will look like a firm, red bump. The healthcare provider will measure the size and firmness of the bump. It is considered positive in the following situations:

• If the bump is greater than or equal to 5 mm, then the person has a compromised immune system.
• If the bump is equal to 10 mm and the person is a healthcare worker.
• If the bump is equal to 15 mm and there are no risk factors.

IGRA Blood Test

A tuberculosis blood test measures the immune response to TB bacteria in a blood sample. A positive tuberculosis blood test indicates a person has been exposed to the bacterium causing TB.

The healthcare provider will order further tests to confirm the active or latent TB. These tests include a chest X-ray or sputum (phlegm) test.

Negative TB Test

Tuberculin Skin Test

A tuberculin skin test is considered negative when there is no bump or a bump less than 5mm at the injection site. This means the person has not been infected with the tuberculosis bacteria.

 IGRA Blood Test

An IGRA blood test is considered negative when it indicates no immune reaction to the TB bacteria. It suggests that the person is not infected with tuberculosis.

 If a person has symptoms of TB but the tuberculosis test results are negative, further testing may be recommended by the doctor.  

Factors That Increase the Risk of Tuberculosis

Almost everybody is at risk of getting infected with tuberculosis, especially if you have come into contact with someone who is infected or have visited a place where many people are infected with tuberculosis. However, individuals who are suffering from latent tuberculosis and do not get treated on time are most likely to develop active tuberculosis. Apart from that, people with a weakened immune system are also at risk of getting infected with tuberculosis. Here are the risk factors: -

HIV Infection (the virus that causes AIDS): People with HIV are more likely to contract TB infection. HIV weakens the immune system, making it harder for the body to fight the TB germs.

Substance Abuse: People who use drugs, especially injected drugs, are at a higher risk of contracting tuberculosis due to a weakened immune system, poor nutrition, and increased exposure to environments where TB spreads easily.

Silicosis: This is a lung disease where inhaling silica dust leads to lung damage. This condition impairs the lung’s ability to clear TB bacteria and increasing the risk.

Diabetes Mellitus: High blood sugar levels can impair immune function, making it harder to fight off TB infections.

Severe Kidney Disease: Chronic Kidney Disease and patients undergoing dialysis are associated with an increased risk of getting tuberculosis.

Low Body Weight: People with low body weight may be malnourished, making it difficult for the body to fight off infections, including TB.  

Organ Transplants: Recipients require immunosuppressive therapy to prevent organ rejection, diminishing the body’s ability to fight TB bacteria.

Head and Neck Cancer: Cancer and its treatment can weaken the immune system, increasing the risk of TB infection.

Medical Treatments: Certain medical treatments, such as long-term use of corticosteroids, can suppress the immune responses, increasing the risk of contracting the TB bacterium.

Specialized Treatment: Biological therapies for rheumatoid arthritis or Crohn’s disease target the immune pathways, weakening the body’s defense against TB. 

How to Reduce the Risk of Tuberculosis?

Individuals may be at a higher risk of tuberculosis if they have recently come in contact with an infected person. They can get a latent tuberculosis blood test for precautionary reasons. Mentioned below are some ways to prevent tuberculosis:

• Get the Bacillus Calmette-Guerin (BCG) vaccination from a medical practitioner
• Take preventive medications as directed if a latent TB infection is present to ensure effective treatment.
• Attend all follow-up appointments for monitoring the treatment progress.
• Do self-isolation when symptoms of TB begin to exhibit.
• Do not travel by public transportation in case of active TB infection.
• Cover the mouth and nose with a tissue or elbow when coughing and sneezing can reduce the transmission.
• Wash hands thoroughly and frequently to prevent the spread of TB bacteria.
• Keep living and working spaces well-ventilated by keeping the windows open or using fans to disperse airborne TB bacteria.
• People with a high risk of developing tuberculosis should undergo regular screenings to detect active infections.
• Maintain a healthy diet, exercise regularly, and avoid smoking to strengthen the immune system, which can help in fighting off the bacteria.