CMLA Specimen Collection & Handling 2 — Questions and Answers
Question 1: Which tube additive is found in a light blue (sodium citrate) tube and is used for coagulation studies?
- EDTA
- Sodium citrate (Correct answer)
- Lithium heparin
- Sodium fluoride
Correct answer: Sodium citrate
Light blue tubes contain sodium citrate, which chelates calcium to prevent clotting and is required for coagulation tests like PT and aPTT.
Question 2: A patient's arm is edematous at the antecubital fossa. What is the most appropriate action?
- Collect from the edematous site using a smaller gauge needle
- Select an alternative site such as the forearm or hand (Correct answer)
- Perform a capillary puncture on the same arm
- Delay the draw until the edema resolves
Correct answer: Select an alternative site such as the forearm or hand
Edematous sites can dilute the specimen with fluid and alter results, so an alternative non-edematous site should be selected.
Question 3: When filling multiple tubes during a venipuncture, which tube should be filled immediately after the blood culture bottle?
- SST (gold/tiger-top)
- EDTA (lavender-top)
- Sodium citrate (light blue) (Correct answer)
- Sodium fluoride (gray-top)
Correct answer: Sodium citrate (light blue)
Per the CLSI order of draw, sodium citrate (light blue) tubes are filled first among additive tubes after blood cultures to avoid cross-contamination with other additives.
Question 4: How long should a tourniquet remain in place before venipuncture to avoid hemoconcentration?
- No more than 1 minute (Correct answer)
- Up to 3 minutes
- Up to 5 minutes
- Time does not matter
Correct answer: No more than 1 minute
Tourniquets should be released within 1 minute to prevent hemoconcentration, which can falsely elevate cell counts and analyte concentrations.
Question 5: Which of the following is the correct angle of needle insertion for a routine adult venipuncture?
- 5–10 degrees
- 15–30 degrees (Correct answer)
- 45 degrees
- 90 degrees
Correct answer: 15–30 degrees
A 15–30 degree angle is standard for venipuncture, allowing the needle to enter the vein without passing through the posterior wall.
Question 6: A gray-top tube contains sodium fluoride. What is the primary purpose of this additive?
- Prevent coagulation for hematology tests
- Inhibit glycolysis to preserve glucose levels (Correct answer)
- Accelerate clot formation for serum chemistry
- Preserve red blood cell morphology
Correct answer: Inhibit glycolysis to preserve glucose levels
Sodium fluoride inhibits glycolytic enzymes, preserving glucose concentrations in the specimen for up to 24 hours.
Question 7: When performing a skin puncture on an infant's heel, which area should be avoided?
- The plantar surface of the heel
- The central posterior curvature of the heel (Correct answer)
- The medial or lateral plantar heel surface
- The lateral aspect of the third or fourth finger
Correct answer: The central posterior curvature of the heel
The central posterior curvature of the heel is too close to the calcaneal bone and risks osteomyelitis; only the medial or lateral plantar surfaces are safe for heel sticks.
CMLA Specimen Collection & Handling 2
Which tube additive is found in a light blue (sodium citrate) tube and is used for coagulation studies?