Search Results: Displaying all QFT Procedure (5)

Question Date Updated
What are the steps in administering the test? 2013 1. It is best to confirm arrangements for testing with a qualified laboratory, which can deliver the necessary sampling pack. 2. Draw a 1 mL sample of blood from a patient directly into each of the three blood collection tubes, following the manufacturer’s instructions. 3. Assure delivery to the laboratory for incubation as soon as possible (and within 16 hours) after blood draw. Keep at room temperature (22±5ºC) before incubation. Or alternatively: at the collection site, incubate the tubes standing upright for 16 to 24 hours at 37ºC before shipping them to the laboratory at room temperature (or refrigerated) within 3 days.
Do the QFT tubes need to be collected in a specific order? 2013 If you are only collecting blood for TB testing, it is advisable to collect 1 mL of blood in the Nil tube followed by the TB antigen tube and finally the Mitogen tube. However if you are also collecting blood for other tests at the same time, the correct order relative to these other tubes may depend on what other tests will be performed.
Why can filling of the tubes occur slowly? 2013 The blood collection tubes are manufactured to draw a 1 mL sample into a 5 mL tube and therefore may fill slowly. In some locations at high altitudes (> 810 m or 2,650 ft) the tubes will not draw sufficient blood (sufficient is close to the indicator line of the tube label). In these situations either use a high altitude QFT tube (QFT-HA) for altitudes between 1,020 m (3,350 ft) and 1,875 m (6,150 ft), or if outside of these altitudes, blood can be collected using alternate collection methods, as described in the QFT Package Insert.
Why it is necessary to shake the tubes immediately after blood collection? 2013 As the tubes only collect 1 mL of blood, thorough mixing is essential to solubilize the tubes’ contents, which are coated on the inner wall. This is best achieved by shaking the tubes ten (10) times, just firmly enough to ensure the entire inner surface of the tube is coated with blood, immediately after filling tubes. Tubes should be between 17 - 25ºC (63 - 77ºF) at the time of blood filling. Over-energetic shaking may cause gel disruption and could lead to aberrant results.
What is the effect of incubating the tubes for longer than the recommended time (ie. if accidently left over the weekend)? 2013 Clinical studies conducted to develop the test cut-off for QFT incubated the tubes for 16–24 hours (as recommended in the QFT Package Insert). Incubating the tubes over 24 hours has not been validated by clinical studies and should be avoided. Another sample will need to be collected.

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