What should you know about a Quantiferon blood test?

Quantiferon, also called an interferon-gamma release assay, is a laboratory blood test for tuberculosis (TB) infection. A sample of blood is exposed to substances associated with TB bacteria, and the laboratory measures an immune response. It is often used when a clinician needs to assess possible latent TB infection or when a skin test may be less suitable.

A positive result suggests TB infection and usually needs clinical review. Your clinician may ask about symptoms, previous TB treatment, exposure, travel, medicines, and immune health. A chest X-ray or other assessment may be needed to distinguish inactive infection from active TB disease.

A negative result makes TB infection less likely, but it may not exclude it after a recent exposure or in someone whose immune response is weakened. An indeterminate or borderline result means the laboratory could not provide a clear answer; repeat testing or another test may be considered. A Quantiferon result does not confirm immunity from a vaccine and does not diagnose every cause of cough or fever.

Most people do not need to fast or change their routine before the blood draw. Tell the clinician if you have had TB, received a TB vaccine, recently spent time with someone with TB, or take medicines that suppress the immune system. Mention recent illness and any difficulty with blood tests.

After the sample is taken, keep the dressing in place as advised and seek the result through the service that ordered the test. Do not assume that a positive result means you can spread TB; infectiousness depends on whether active disease is present and where it affects the body. Follow-up is particularly important if you have symptoms or a weakened immune system.

Contact the clinician who arranged the test promptly if the result is positive, indeterminate, or unclear, especially after a known TB exposure. Arrange medical assessment for a cough that persists, coughing blood, unexplained weight loss, fever, night sweats, or marked tiredness.

Seek urgent help for severe breathing difficulty, chest pain, confusion, or coughing a large amount of blood. These symptoms need prompt assessment regardless of the Quantiferon result.

Ask what your result was, whether your exposure history changes its interpretation, and whether you need a chest X-ray or another assessment. If the result is positive, ask whether the findings suggest latent infection or active disease and what follow-up is planned.