Quantiferon TB Gold®

Quantiferon (TB) Blood Testing

Quantiferon TB Gold® test is a screening test for Tuberculosis. It is a type of IGRA test (Interferon Gamma Release Assay). The test measures the cell-mediated responses to antigens of Mycobacterium tuberculosis. Quantiferon testing was FDA approved in 2001. The test involves having a blood sample taken and sending the specimen to the lab for analysis.

The Quantiferon test can be used as an alternative to either a one step or two step Tuberculosis skin test. Like a tb skin test, the Quantiferon does not distinguish between active or inactive TB. The most recent guidelines from the CDC recommend Quantiferon in most situations.

Tuberculosis screening is often required for health care workers, students, immigration medical exams, international travelers and other people who may be at risk. Sometimes, the tuberculosis skin test is inconvenient due to the need to return in 48-72 hours to have the injection site checked.

Like tb skin testing, live vaccines may interfere with the Quantiferon test results. The CDC recommends the Quantiferon be given either on the same day as live-virus vaccines or at least 4 weeks after live vaccines. Live-virus vaccines include MMR, Varicella, Shingles, Yellow Fever, Smallpox and Intranasal Influenza.

Advantages of the Quantiferon TB Gold® include:

  • Not needing to return for the test results like the tb skin test which requires 2 visits (we can send the results to you, your school or work)
  • BCG vaccine will not cause a false positive in Quantiferon test as it sometimes does with a TB Skin test
  • Results are usually available in 3-5 business days
  • Can be used in all circumstances in which a TB Skin test is recommended

Limitations of the Quantiferon TB Gold® include:

  • Not recommended in children 5 years old
  • Limited data on immunocompromised individuals
  • Persons very recently exposed to TB

After Testing

Results will be reported as:
  1. Negative (Normal)
  2. Indeterminate (the test was unable to determine a result of negative or positive and the test should be repeated with a new blood sample)
  3. Positive (Abnormal)

Diagnosis of Tuberculosis

Diagnosis of Tuberculosis infection and decisions about personal or public health should be based on other clinical information as well as Quantiferon results.

If you have a positive Quantiferon result, you should be evaluated for the likelihood of progression to active Tuberculosis by either the public health Tuberculosis Clinic or your Primary Care Provider and a Chest x-ray.

TB Skin Testing

A TB skin test is used to determine if a person already has immunity to the Tuberculosis bacteria. This can occur if someone has TB, if they were exposed to TB in the past, or if they received the BCG vaccine. A liquid is injected in the top layers of skin on the forearm, and the injection site is checked 48-72 hours later for a specific reaction.

Read More About TB Skin Testing