CPHT Order of Draw & Tube Additives 2 — Questions and Answers
Question 1: What is the correct CLSI-recommended order of draw when collecting multiple tubes via venipuncture?
- EDTA → Citrate → Blood cultures → Serum → Heparin
- Blood cultures → Citrate → Serum/SST → Heparin → EDTA → Fluoride (Correct answer)
- Serum → Citrate → Heparin → EDTA → Fluoride
- Citrate → Blood cultures → Serum → EDTA → Heparin
Correct answer: Blood cultures → Citrate → Serum/SST → Heparin → EDTA → Fluoride
The CLSI-recommended order is blood cultures first, then citrate, serum/SST, heparin, EDTA, and finally fluoride/oxalate tubes to prevent additive carryover between tubes.
Question 2: Why must blood culture bottles be collected before all other tubes in the order of draw?
- They require the largest blood volume
- To prevent contamination from tube additives and maintain sterility (Correct answer)
- They must be incubated immediately after collection
- Their anticoagulant degrades fastest at room temperature
Correct answer: To prevent contamination from tube additives and maintain sterility
Blood culture bottles are collected first to ensure no tube additive carryover contaminates the sterile culture medium, which could cause false-positive or false-negative microbiology results.
Question 3: Why is the light blue (sodium citrate) tube collected before serum tubes in the standard order of draw?
- Citrate tubes require more inversion steps and take longer to process
- Clot activator from serum tubes could carry over and falsely affect coagulation results (Correct answer)
- Citrate tubes are more fragile and break if agitated by later draws
- Sodium citrate expires more quickly than other tube additives
Correct answer: Clot activator from serum tubes could carry over and falsely affect coagulation results
If serum/SST tubes were collected first, silica clot activator particles could carry over into the citrate tube on the needle and artificially activate coagulation, falsifying PT/INR results.
Question 4: When using a butterfly/winged infusion set, what must be done before collecting a sodium citrate tube?
- Flush the tubing with normal saline first
- Draw a discard tube to eliminate air from the tubing (Correct answer)
- Fill the citrate tube halfway, pause 30 seconds, then complete filling
- Switch to a straight needle instead of a butterfly for citrate tubes
Correct answer: Draw a discard tube to eliminate air from the tubing
The dead space air in the butterfly tubing must be displaced with blood using a discard tube; otherwise, underfilling disrupts the critical 9:1 blood-to-sodium-citrate ratio needed for coagulation accuracy.
Question 5: In the order of draw, EDTA (lavender) tubes are collected immediately before which tube type?
- Blood culture bottles
- Serum separator tubes (SST)
- Heparin (green) tubes
- Fluoride/oxalate (gray) tubes (Correct answer)
Correct answer: Fluoride/oxalate (gray) tubes
EDTA tubes are collected before fluoride/oxalate (gray) tubes, as gray tops are always the last tube in the standard CLSI order of draw sequence.
Question 6: What is the primary reason for following a specific order of draw during multi-tube collection?
- To ensure tubes are collected as quickly as possible
- To prevent additive carryover that could produce erroneous test results (Correct answer)
- To guarantee all tubes are completely filled to the fill line
- To minimize the risk of hemolysis in all tubes equally
Correct answer: To prevent additive carryover that could produce erroneous test results
Following the correct order of draw prevents cross-contamination of tube additives, which can cause significant errors such as artificially low calcium when EDTA carries over into chemistry tubes.
Question 7: A phlebotomist needs to collect a CBC, a BMP, and a PT/INR. What is the correct tube drawing order?
- Lavender (EDTA), Gold (SST), Light Blue (Citrate)
- Light Blue (Citrate), Gold (SST), Lavender (EDTA) (Correct answer)
- Gold (SST), Light Blue (Citrate), Lavender (EDTA)
- Gold (SST), Lavender (EDTA), Light Blue (Citrate)
Correct answer: Light Blue (Citrate), Gold (SST), Lavender (EDTA)
The correct order is light blue (citrate) for PT/INR, then gold SST for BMP, then lavender EDTA for CBC, following the standard CLSI order of draw.
CPHT Order of Draw & Tube Additives 2
What is the correct CLSI-recommended order of draw when collecting multiple tubes via venipuncture?