QuantiFERON(r)-TB

Main Line Hospitals – Laboratory Services is pleased to announce now offers in-house testing for QuantiFERON®-TB, a blood test for M. tuberculosis (TB) infection, effective Tuesday March 2, 2010.  This test is at least as sensitive as the PPD skin test, gives fewer false positive results, and does not require the patient to return as the skin test does. 

QuantiFERON®-TB is unaffected by Bacille Calmette-Guerin (BCG) vaccination and most environmental non-tuberculous mycobacteria (except M. kansasii, M. marinum, and M. szulgai).  A positive result is strongly predictive of true infection with M. tuberculosis.  QuantiFERON®-TB is intended for use in conjunction with risk assessment, radiography, and other medical and diagnostic evaluations.  The test may be ordered as “QuantiFERON-TB”. 

The QuantiFERON®-TB assay is a qualitative test of infection.  It measures the production of interferon-gamma by effector T-cells in response to TB peptide antigens.  Effector T-cells are considered to be present only during current infection, but not in old/cured infection.  A positive result suggests that current M. tuberculosis infection is likely, whether active disease or latent TB infection.  A negative result suggests that M. tuberculosis is unlikely but cannot be totally excluded, especially when the illness is consistent with tuberculosis or the likelihood of progression to disease is increased (e.g. because of immune suppression).  In rare cases results cannot be interpreted, as the blood cells have not responded to a positive control stimulant.  This indicates the sample may have been mishandled or that the patient's immune system is not functioning well.  These results are called "indeterminate"; TB infection can neither be excluded nor confirmed.

The QuantiFERON®-TB assay requires special blood collection tubes available from hospital storerooms or, for office patients, from Main Line Hospitals – Laboratory Services Client Servicesat 484-580-4200.  These specialized blood collection tubes, one (1) each of Nil Control, TB Antigen, and Mitogen, are used to collect whole blood via venipuncture, and contain antigens representing certain M. tuberculosis proteins or controls.  Incubation of the blood occurs in the tubes for 16 to 24 hours, after which plasma is harvested and tested for the presence of interferon-gamma. 

To obtain optimal results, the tubes must be shaken vigorously for 5 seconds to ensure that the entire inner surface of the tube has been coated with blood.  Proper shaking will lead to frothing of the blood. The tubes must arrive in the lab as soon as possible after collection (within 16 hours), and before 3:30pm Monday through Friday only. 

If you have any questions or concerns please feel free to contact Albert A. Keshgegian, MD, PhD, Medical Director, at 484-476-3552, or Annemarie Brewer, Immunology Supervisor, at 484-476-8408.