CMT Laboratory Procedures and Specimen Collection 1 — Questions and Answers
Question 1: Which evacuated tube color is used for coagulation studies such as PT and PTT?
- Red
- Light blue (Correct answer)
- Lavender
- Green
Correct answer: Light blue
Light blue (sodium citrate) tubes are used for coagulation studies because citrate binds calcium to prevent clotting while preserving clotting factor activity.
Question 2: According to the CLSI order of draw, which tube should be collected FIRST when multiple tubes are needed?
- EDTA (lavender) tube
- SST (gold) tube
- Blood culture bottles (Correct answer)
- Sodium citrate (light blue) tube
Correct answer: Blood culture bottles
Blood culture bottles are drawn first to minimize the risk of contamination from skin flora and additives in other tubes.
Question 3: A tourniquet should be applied no longer than how many minutes before venipuncture to prevent hemoconcentration?
- 30 seconds
- 1 minute (Correct answer)
- 2 minutes
- 5 minutes
Correct answer: 1 minute
A tourniquet left on longer than 1 minute causes hemoconcentration and falsely elevated results for proteins, enzymes, and cellular components.
Question 4: Which of the following actions is the MOST common cause of hemolysis during venipuncture?
- Using a large-bore needle
- Mixing tubes too vigorously (Correct answer)
- Collecting from an antecubital vein
- Applying the tourniquet correctly
Correct answer: Mixing tubes too vigorously
Vigorous mixing of tubes breaks red blood cell membranes, releasing intracellular contents and causing hemolysis that can interfere with test results.
Question 5: A capillary puncture on an adult finger should be performed on which part of the fingertip?
- Center of the fingertip pad
- Side of the middle or ring finger (Correct answer)
- Tip of the index finger
- Base of the thumb
Correct answer: Side of the middle or ring finger
The lateral (side) aspect of the middle or ring finger is the preferred site because it has adequate capillary beds and avoids nerves and bone centrally located in the fingertip.
Question 6: Which tube additive prevents glycolysis and preserves glucose levels in a specimen?
- EDTA
- Sodium heparin
- Sodium fluoride/potassium oxalate (Correct answer)
- Sodium citrate
Correct answer: Sodium fluoride/potassium oxalate
Sodium fluoride inhibits the enzyme enolase to stop glycolysis, while potassium oxalate acts as an anticoagulant, making this tube the standard choice for glucose testing.
Question 7: When collecting a blood culture, the venipuncture site should be cleaned with:
- 70% isopropyl alcohol only
- Soap and water followed by alcohol
- Chlorhexidine gluconate or iodine tincture after an initial alcohol scrub (Correct answer)
- Povidone-iodine only
Correct answer: Chlorhexidine gluconate or iodine tincture after an initial alcohol scrub
Blood cultures require a two-step disinfection — an initial 70% alcohol scrub followed by chlorhexidine gluconate or iodine tincture — to achieve maximum reduction in skin flora contamination.
CMT Laboratory Procedures and Specimen Collection 1
Which evacuated tube color is used for coagulation studies such as PT and PTT?