TB Gamma Interferon Testing (Quantiferon – TB Gold)
Requests for gamma interferon testing for TB immunity will be via a Consultant Medical Microbiologist only unless requested by Rheumatology or Dermatology outpatient departments.
The TB gold blood collection kit is a single patient pack issued only by the Microbiology laboratory and contains four blood collection tubes, a 21G needle, a safety tube holder and an instruction sheet.
Please notify the Microbiology department prior to sending TB-Gold samples to the laboratory as there are strict incubation times that must be adhered to.
Procedure for taking Quantiferon TB Gold specimens
- Ensure that tubes are at room temperature (17-25°C) before filling.
- For each patient collect 1ml of blood by venepuncture directly into each of the 3 Quantiferon collection tubes.
Note 1. 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.
Note 2.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 to 1.2ml. If the level of blood in any tube is not close to the indicator line, it is recommended to repeat the test.
- 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.
- Immediately after filling tubes, shake them 10 times just firmly enough to ensure the entire inner surface of the tube is coated with blood. NB. Over-energetic shaking may cause gel disruption and could lead to aberrant results.
- Label the tubes appropriately and complete a Microbiology request form.
- The tubes and request form must be sent to the Microbiology laboratory within 16 hours of collection. Do not refrigerate or freeze the blood samples.