Quantiferon TB Gold Test Result Interpretation

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Posted: Feb 22nd, 2022 at 12:00AM - by Ashlee Arnold/Vice President

The QuantiFERON TB Gold Test is a medical test that screens for tuberculosis (TB). It’s an Interferon Gamma Release Assay (IGRA) test that involves taking a blood sample which will then be analyzed in a lab. The QuantiFERON TB Gold test was approved by the Food and Drug Administration in 2011 and functions as an alternative to a one-step or two-step TB Skin Test (TST). It does not distinguish between active and inactive tuberculosis.

TB testing is normally mandated for students, healthcare workers, international travelers, those taking immigration medical exams, and others who may be vulnerable.

According to the CDC, the QuantiFERON TB Gold test can be used in all cases that would typically require a TST. However, as with a TST, there is a possibility that live vaccines might affect the test results of the QuantiFERON TB Gold test. As such, the CDC has advised that the QuantiFERON test be done either on the same day that the live vaccine is administered or a minimum of four weeks after. Some examples of live vaccines are varicella, MMR, yellow fever, and intranasal influenza.

Let's dive into the pros and cons and result interpretations of the QuantiFERON TB Gold test, as well as more information on tuberculosis.

Advantages and Limitations of the QuantiFERON TB Gold Test

As with most medical processes, the QuantiFERON TB Gold test has its pros and cons. If you are suspected to have TB and your doctor recommends that you undergo this test, keep in mind its advantages and limitations:

Advantages:

• Unlike a TB skin test, which needs two visits, you don’t have to go back to the testing facility for your test results. They can be sent to you directly, or to your school or workplace.
• The results are typically released within three to five business days.
• The results are valid for all cases that would normally need a TB skin test.
• Unlike a TB skin test, the BCG vaccine will not render false positives in a QuantiFERON TB Gold test.

Limitations:

• It's not recommended for children who are under five years old (under two years old for immigration requirements).
• It may render inaccurate results for people who were recently exposed to TB.
• There is limited information on its suitability for those who are immunocompromised.

Interpretation of the QuantiFERON TB Gold Test Results

After the blood sample is taken and analyzed, the QuantiFERON TB Gold test will render one of the following results:

• Negative or Normal
• Positive or Abnormal
• Indeterminate, which means that the test could not give a definitive negative or positive result. In this case, generally, the test must be retaken with a fresh blood sample.

However, the QuantiFERON TB Gold test alone does not confirm the diagnosis of tuberculosis infection. The diagnosis is evaluated and decided upon by a medical professional based on the test results, as well as other clinical information. Patients who receive a positive test result should be evaluated by a medical professional to see if they are likely to progress to active TB. They may also be recommended to undergo a chest x-ray.

What is Tuberculosis?

Tuberculosis, or TB, is a highly contagious and infectious airborne disease that affects the respiratory system, particularly the lungs. It can also infect other parts of the body such as the bones, brain, eyes, and lymph nodes. It spreads from one person to another via tiny water droplets which are excreted into the air when an infected person coughs or sneezes.

TB is a severe illness with fatal consequences. According to the World Health Organization, it caused approximately 1.5 million deaths in 2020. In high-risk countries, TB is the second most infectious killer, just behind COVID-19, and is the 13th leading cause of death worldwide.

Tuberculosis is generally rare in developed countries, but not impossible. TB infections increased in 1985, partly due to the rise of HIV, which weakens the immune system and prevents it from eliminating the TB bacteria. It decreased again in the U.S. in 1993 but is still a concern as tuberculosis cases can re-emerge.

Latent vs Active Tuberculosis

There are two types of tuberculosis – latent TB and active TB. The QuantiFERON TB Gold test does not distinguish between these two, but they differ based on how they manifest in an infected person. This is because everyone's immune systems are different. Some can appear more, or less, sick than others.

Latent TB is when you are infected with tuberculosis, but you are not exhibiting any symptoms because the bacteria residing in your body is inactive. Also referred to as inactive TB or a TB infection, this type of tuberculosis is not contagious. However, there is a possibility that the bacteria can become active, so it's still crucial for someone with latent TB to seek guidance from a medical provider.

Active TB, on the other hand, is when you are infected with the bacteria and show symptoms of the illness. Also referred to as TB disease, this type of tuberculosis is contagious. Latent TB can become active TB after several weeks, or even years, after infection.

Signs and Symptoms of Tuberculosis

A person with active tuberculosis may exhibit the following symptoms:

• Prolonged sputum-producing cough which lasts over three weeks
• Experiencing chest pains or pain while breathing and coughing
• Lack of appetite and consequent unintentional loss of weight
• Chills
• Fever
• Night sweats
• Fatigue

Additionally, some may experience symptoms that indicate what organs the TB has infected. For example, coughing up mucus or blood may point to TB infection in the lungs, and experiencing bone pain might mean that it has infected the bones.

Because these symptoms are also common for other illnesses, it's best to see a clinician to be properly diagnosed and treated.

If you have come in close contact with someone with tuberculosis, or are suspected to have TB and advised by your doctor to get tested, schedule an appointment with e7 Health.

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