CMLA Specimen Collection & Processing 1 — Questions and Answers
Question 1: What is the correct order of draw when collecting multiple blood tubes using a vacutainer system?
- Blood cultures → light blue → red/SST → green → lavender → gray (Correct answer)
- Lavender → light blue → red/SST → green → blood cultures → gray
- Red/SST → light blue → blood cultures → lavender → green → gray
- Light blue → blood cultures → green → lavender → red/SST → gray
Correct answer: Blood cultures → light blue → red/SST → green → lavender → gray
The CLSI-recommended order of draw begins with blood cultures (sterile), followed by light blue (coagulation), then serum tubes, heparin, EDTA, and finally fluoride/oxalate to prevent additive carryover between tubes.
Question 2: Which evacuated tube color is used for coagulation studies such as PT and aPTT?
- Lavender (EDTA)
- Light blue (sodium citrate) (Correct answer)
- Green (heparin)
- Gold/SST (clot activator)
Correct answer: Light blue (sodium citrate)
Light blue tubes contain sodium citrate, which binds calcium and prevents clotting; the 9:1 blood-to-anticoagulant ratio is critical for accurate coagulation assays like PT and aPTT.
Question 3: At what angle should the needle be inserted when performing a standard venipuncture?
- 5–10 degrees
- 15–30 degrees (Correct answer)
- 45–60 degrees
- 70–90 degrees
Correct answer: 15–30 degrees
A 15–30 degree angle (bevel up) allows the needle to enter the vein smoothly without passing through the posterior wall, minimizing trauma and hematoma formation.
Question 4: How long should a tourniquet remain applied during blood collection to prevent hemoconcentration?
- No more than 1 minute (Correct answer)
- 2–3 minutes
- Up to 5 minutes
- As long as needed to locate the vein
Correct answer: No more than 1 minute
A tourniquet left on for more than 1 minute causes hemoconcentration and may affect results for potassium, proteins, and other analytes by restricting blood flow.
Question 5: Which additive is found in lavender (purple) top tubes and is used for most hematology testing?
- Sodium citrate
- Sodium fluoride
- EDTA (ethylenediaminetetraacetic acid) (Correct answer)
- Lithium heparin
Correct answer: EDTA (ethylenediaminetetraacetic acid)
EDTA chelates calcium ions to prevent coagulation and preserves cell morphology, making lavender tubes the standard choice for CBC and differential count.
Question 6: What is the proper procedure for labeling a blood specimen?
- Label the tube before leaving the patient's room to save time
- Label the tube at the patient's side immediately after collection, verifying the patient's identity (Correct answer)
- Label the tube upon arrival at the laboratory to prevent smearing
- Allow the patient to write their own name on the label for accuracy
Correct answer: Label the tube at the patient's side immediately after collection, verifying the patient's identity
CLSI standards require specimens to be labeled at the bedside immediately after collection, with the phlebotomist verifying two patient identifiers to prevent specimen mislabeling errors.
Question 7: Which tube color contains thrombin or clot activator plus a gel barrier and is used for serum chemistry testing?
- Light blue
- Lavender
- Gold or SST (serum separator tube) (Correct answer)
- Gray
Correct answer: Gold or SST (serum separator tube)
Gold or tiger-top SST tubes contain a clot activator to speed clot formation and a gel that separates serum from cells during centrifugation, making them ideal for most serum chemistry panels.
CMLA Specimen Collection & Processing 1
What is the correct order of draw when collecting multiple blood tubes using a vacutainer system?