TB Quantiferon gold test (mycobacteria mycobacterium tuberculosis mtb latent igra gamma interferon)

• This is a whole-blood test for use as an aid in diagnosing Mycobacterium tuberculosis infection, including latent tuberculosis infection and tuberculosis disease.
• The test is only available after discussion with a Consultant Microbiologist.
• The test can be used in all circumstances in which the tuberculin skin test is currently used. However, caution should be used when testing certain populations because of limited data. These include:
  • Children younger than 17 years of age
  • Persons recently exposed to M. tuberculosis
  • Immunocompromised persons (e.g.impaired immune function caused by HIV infection or acquired immunodeficiency syndrome [AIDS], current treatment with immunosuppressive drugs, selected haematological disorders, specific malignancies, diabetes, silicosis, and chronic renal failure).
• Various steps in the processing of these specimens are time critical. Therefore samples can only be taken on a Monday, Tuesday or Wednesday and must be received in the laboratory before 5.00pm on the same day. If taken in Cheltenham, please allow time for transport to Gloucester.
• See also:
  • TB T-Spot test
  • Mycobacterium and TB investigations

Sample requirements

QuantiFERON -TB Gold test kits are available from the Microbiology Laboratory on a named patient basis

A specimen collection protocol sheet is provided with the kit.

Collection method

• The kit contains 4 collection tubes:
  • Grey cap: Nil control
  • Green cap: TB antigen 1
  • Yellow cap: TB antigen 2
  • Purple cap: Mitogen control
• For each patient collect 1ml of blood by venepuncture directly into each of the 4 Quantiferon collection tubes.
• 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.
• As the 1ml 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 1ml fill volume. This method has been validated for volumes ranging from 0.8 – 1.2ml. If the level of blood in any tube is not close to the indicator line, another sample should be obtained.
• Mix the tubes by turning the tube end over end 8-10 times or shaking the tube for 5 seconds ensuring that the entire inner surface of the tube has been coated with the blood. Thorough mixing is required to ensure complete mixing of the blood with the tube’s contents.
• Label the tubes and send to the Microbiology Laboratory immediately.

Required information

• Relevant clinical details
• Whether test is being performed to screen for suspected latency (asymptomatic) or for current, active TB infection
• M. tuberculosis exposure history
• Immunocompromise
• If test is being performed prior to immunosuppressive treatment
• If patient is a healthcare worker
• Please inform the laboratory when the sample is being sent

Storage/transport

Transport to the Microbiology laboratory the same day as samples have to be incubated as soon as possible and must be received in the laboratory before 5.00pm

Do not freeze or refrigerate the blood samples

Turnaround time

Sent to a National Reference Centre

Up to 2 weeks