Tuberculosis Testing - What is the QuantiFERON-TB Test?

In 2001, the Food and Drug Administration (FDA) approved the tuberculosis test called QuantiFERON-TB (QFT). This tuberculosis test measures the release of interferon-gamma (IFN-g) in whole blood in response to stimulation of the purified protein derivative from M. tuberculosis. In laymen's terms, the QFT tuberculosis test measures a person's immune reactivity to Mycobacterium tuberculosis, the bacterium that causes tuberculosis.

How Does the QFT Tuberculosis Test Work?

A blood sample is drawn from the patient. The blood is mixed with antigens - the protein substances that produce an immune response - and controls. The antigens include tuberculin, which is purified protein derivative (PPD) from M. tuberculosis, and avian sensitin, which is purified protein derivative from My avium complex. Then the blood is incubated for 16 to 24 hours.

At the end of the incubation period, the QFT tuberculosis test is read. If the patient tests positive for tuberculosis, i.e. the patient is infected with M. tuberculosis, the blood cells would have released a larger proportion of IFN-g in response to the tuberculin than that released in response to the avian sensitin or the controls. However, in order to confirm or exclude a tuberculosis diagnosis, additional testing, such as a chest x-ray, is required. (Read What You Need to Know Before Getting A Chest X-Ray)

Advantages of QFT Tuberculosis Test

Only one doctor visit is required

The test assesses responses to multiple antigens simultaneously

Eliminates the concern of the booster phenomenon as seen with the PPD tuberculosis skin test

Reduced risk of testing interpretation errors and bias

Disadvantages of QFT Tuberculosis Test

Time limit (12 hours) for testing of the drawn blood

Limited knowledge and experience with QFT tuberculosis test

The QFT's ability to predict the progression of tuberculosis infection to tuberculosis disease has not been evaluated

Additional testing required to confirm or exclude tuberculosis diagnosis

Source: CDC