Quantiferon Test: Don’t Use It Alone to Detect Active TB

In 2004, the U.S. FDA approved the Quantiferon-TB Gold (QFT-G) assay, which measures release of the cytokine interferon-γ (IFN-γ) from blood cells after stimulation with two synthetic peptides derived from Mycobacterium tuberculosis. This assay has a high specificity in detecting M. tuberculosis infection, but what is its sensitivity in detecting active disease among patients with suspected TB? To find out, researchers reviewed the records of 242 patients who were tested using the QFT-G at the San Francisco Department of Public Health Tuberculosis Clinic.

Of the 45 patients subsequently diagnosed with active TB, the QFT-G was positive in 25 (55%), negative in 17 (38%), and indeterminate in 3 (7%). When indeterminate results were excluded, th…