NHA Certified Phlebotomy Technician (CPT)Collection RoutineHard
A phlebotomy technician needs to collect blood for a prothrombin time (PT) and activated partial thromboplastin time (aPTT) test. The patient has difficult veins, and the technician anticipates a difficult draw. Which of the following is the correct order of draw for these specific tubes if collected via a winged infusion set with a discard tube?
- ALight blue, then red top.
- BRed top, then light blue.
- CDiscard tube, then light blue.
- DLight blue, then discard tube.
Show answer & explanationAnswer & explanation
Correct answer: C. Discard tube, then light blue.
When using a winged infusion set (butterfly needle) for coagulation tests (light blue top), a discard tube must be drawn first. The air in the tubing of the butterfly set can cause underfilling of the light blue top tube, leading to an incorrect blood-to-anticoagulant ratio and inaccurate results. The discard tube removes this air.
Why the other options are wrong
- A. A red top tube is not typically used as a discard tube for coagulation tests, nor is it the correct primary tube if PT/aPTT are the only tests.
- B. Similar to option C, this order is incorrect for ensuring proper coagulation specimen integrity with a butterfly needle.
- D. Drawing the light blue tube first would result in an underfilled tube due to air in the butterfly tubing, compromising the specimen.
Discard Tube for Coagulation Tests
A tube collected prior to a light blue top (coagulation) tube when using a winged infusion set to remove air from the tubing and ensure proper fill volume.
- Only necessary with butterfly needles.
- Prevents underfilling of light blue top tubes.
- Ensures correct anticoagulant-to-blood ratio.
Memory trick: Butterfly's air is a snare, discard first, then blue, no despair.