Blood Test Preferable to Skin Test for TB Diagnosis

Results of the blood test are ready within 24 hours and do not require a return visit from the patient.

Interferon Gamma Release Assays (IGRAs) are simple blood tests that accurately identify people infected with Mycobacterium tuberculosis, the causative agent of TB. Unlike the TST, where the results are open to interpretation, IGRAs are accurate, sensitive, and specific for the disease. The guidelines recommend the assay over the TST for testing persons who have received Bacille Calmette-Guerin (BCG) injections, as a vaccine or for cancer therapy. Another reason for the preference is for diagnosing TB infection for persons from groups that historically have low rates of returning to have TSTs read. IGRAs may be used in place of TST (without preference) to test recent contacts of persons with infectious TB or for periodic screening to address occupational exposure to TB.

The QuantiFERON-TB Gold Test (QFT) is an IGRA manufactured by Cellestis International Pty Ltd. (Chadstone, Australia). QFT is available for use in all clinical settings in which TST is commonly used. Examples include contact tracing, regular employee testing, for example for health care workers, as well as screening programs for prisoners and immigrants. QFT's application in the screening of immunosuppressed patients prior to antitumor necrosis factor-alpha therapy initiation and in patients with human immunodeficiency virus (HIV), cancer, or organ transplants offers distinct advantages over the TST.

Antonino Catanzaro, M.D., professor of medicine, University of California (UCSD; San Diego, USA), said, "These guidelines encapsulate the enormous body of clinical evidence on the performance of the QFT test and reflect the significant benefits this test is bringing to TB control worldwide." It is estimated that one person dies of TB every 17 seconds, causing nearly two million deaths annually. Multi-drug resistant TB is becoming an increasing problem worldwide.

Related Links:
[U.S.] Centers for Disease Control and Prevention
Cellestis International Pty Ltd.
University of California San Diego