ASCP - Phlebotomy Technician Order of Draw and Additives Questions and Answers — Questions and Answers
Question 1: A phlebotomist needs to collect a CBC, a PT, and a glucose test. Which of the following represents the correct order of draw?
- Light blue, lavender, gray (Correct answer)
- Lavender, gray, light blue
- Gray, light blue, lavender
- Light blue, gray, lavender
Correct answer: Light blue, lavender, gray
The correct order of draw as established by the CLSI is: blood cultures, light blue (sodium citrate), serum tubes (red/gold), heparin tubes (green), EDTA tubes (lavender), and finally glycolytic inhibitor tubes (gray). Therefore, the PT test in the light blue top tube must be drawn first, followed by the CBC in the lavender tube, and lastly the glucose test in the gray tube.
Question 2: Which additive is present in a lavender top tube and what is its primary function?
- Sodium Citrate; to perform coagulation studies
- Silica; to activate clotting
- EDTA; to prevent clotting by binding calcium (Correct answer)
- Sodium Fluoride; to inhibit glycolysis
Correct answer: EDTA; to prevent clotting by binding calcium
Lavender top tubes contain Ethylenediaminetetraacetic acid (EDTA), which is an anticoagulant that works by chelating (binding) calcium ions, an essential component for blood clotting. This action preserves the blood cells for hematology tests like a Complete Blood Count (CBC).
Question 3: A phlebotomist is tasked with drawing blood for a STAT chemistry panel. Which color tube, containing which additive, would be most appropriate?
- Light blue top; Sodium Citrate
- Green top; Heparin (Correct answer)
- Gray top; Potassium Oxalate
- Red top; No additive
Correct answer: Green top; Heparin
Green top tubes contain heparin (either sodium or lithium), which is an anticoagulant that inhibits thrombin formation. This allows for rapid separation of plasma for STAT chemistry tests, as there is no need to wait for the blood to clot.
Question 4: During a multi-tube draw, a phlebotomist draws a lavender top tube before a light blue top tube. What is the most likely consequence of this error?
- The glucose level in the light blue tube will be falsely elevated.
- The potassium level in the light blue tube will be falsely decreased.
- The clotting time in the light blue tube may be falsely prolonged. (Correct answer)
- The red blood cell count in the lavender tube will be inaccurate.
Correct answer: The clotting time in the light blue tube may be falsely prolonged.
The additive in the lavender tube is EDTA, which binds calcium. The light blue tube is used for coagulation studies (like PT/PTT) which depend on calcium. If EDTA from the lavender tube contaminates the light blue tube, it will bind the calcium in the sample, leading to artificially prolonged clotting times.
Question 5: Which of the following tubes contains an additive that acts as a glycolytic inhibitor?
- Serum Separator Tube (SST)
- Lavender top tube
- Gray top tube (Correct answer)
- Green top tube
Correct answer: Gray top tube
Gray top tubes contain sodium fluoride, which is a glycolytic inhibitor, meaning it prevents the breakdown of glucose by blood cells. They also typically contain potassium oxalate, an anticoagulant. This combination makes them ideal for glucose testing, especially when analysis may be delayed.
Question 6: A physician orders blood cultures, a coagulation test, and a complete blood count. To prevent cross-contamination, what is the first tube the phlebotomist should draw?
- Light blue top tube
- Lavender top tube
- Red top tube
- Blood culture bottles (Correct answer)
Correct answer: Blood culture bottles
The established order of draw always begins with sterile specimens to prevent microbial contamination. Therefore, blood culture bottles or sterile yellow-top tubes must be collected before any other tubes.
ASCP - Phlebotomy Technician Order of Draw and Additives Questions and Answers
A phlebotomist needs to collect a CBC, a PT, and a glucose test.
Which of the following represents the correct order of draw?