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Alias: TB, Mycobacteria tuberculosis, QFT-Plus

Discipline: Virology

Test information: QFT-Plus is an indirect test for Mycobacteria tuberculosis infection (including disease) and is intended for use in conjunction with risk assessment, radiography, and other medical and diagnostic evaluations.

Availability: Referred to Royal Devon and Exeter NHS Foundation Trust: Monday - Friday during routine hours: 08:45 - 17:15.

Turnaround Time: 7 - 14 Days upon receipt at Royal Devon and Exeter NHS Foundation Trust (batched and run on alternate weeks).

Related Tests: Mycobacterium (Microscopy & Culture)

Specimen Type(s)
  • Blood;
Other Acceptable Specimen Type(s)
Specimen Container - Adult
  • Special kit obtained from the lab;
Specimen Container - Paediatric
  • N/A;
  • N/A;
Part of a test profile?
Volume (min) of sample to be sent to laboratory
For each patient collect 1 mL of blood by venepuncture directly into each of the 4 QuantiFERON collection tubes.
Patient Preparation, Sample Handling and Transport
  • If a 'butterfly needle' is being used to collect blood, a purge tube should be used to ensure that the tubing is filled with blood prior to the QuantiFERON-TB tubes being used.
  • Do not refrigerate these specimens.
  • As the 1 mL tubes draw blood relatively slowly, keep the tube on the needle for 2-3 seconds once the tube appears to have completed filling to ensure the correct volume is drawn.
  • The black mark on the side of the tubes indicates the 1 mL fill volume. This method has been validated for volumes ranging from 0.8 to 1.2 mL. If the level of blood in any tube is not close to the indicator line, it is recommended to obtain another sample.
  • Bring directly to the laboratory (not via porters) on the day the sample has been taken.
  • Prior to incubation, maintain the tubes at room temperature (22 °C ± 5 °C). Samples need to be transferred to a 37 °C incubator as soon as possible, and within 16 hours of collection.
  • Do not send to laboratory after 4.30pm due to processing time required.
  • Tubes are available from the Microbiology (telephone 01872 254900). They are only issued to Respiratory Medicine, Paediatrics (respiratory), Gastroenterology and Rheumatology, Occupational Health and to General Practice.
  • Immediately after filling tubes, gently invert each 10 times to ensure the entire inner surface of the tube is coated with blood, to solubilise antigens on tube walls.
Maximum add on time
Units and Reference Ranges / Interpretation
Negative / Indeterminate / Positive

The test cannot distinguish between active and latent infection so should be used in conjunction with other disease markers.

A negative QuantiFERON result does not rule out possibility of Mycobacterium tuberculosis infection. False negative results may be due to incorrect handling of the blood collection tubes. Negative results may also occur, in spite of infection, in patients with an impaired immune response, or very early in infection - before T cell mediated response has developed.

Patients who are immunosuppressed from medical conditions or treatment may have insufficient lymphocytes present to give a mitogen response.

UKAS number
UKAS accredited test?

If you have any queries about a test or results interpretation please contact us.

Last updated: 06-06-2023