Phlebotomy Order of Draw and Additives Questions and Answers 1 — Questions and Answers
Question 1: A phlebotomist needs to draw blood for a coagulation test, a complete blood count (CBC), and a serum chemistry panel. Which of the following represents the correct order of draw?
- Light Blue, Lavender, Red
- Red, Lavender, Light Blue
- Lavender, Red, Light Blue
- Light Blue, Red, Lavender (Correct answer)
Correct answer: Light Blue, Red, Lavender
The correct order of draw according to CLSI guidelines is: 1. Blood cultures, 2. Light Blue (sodium citrate for coagulation), 3. Red/Gold/Tiger Top (serum tubes), 4. Green (heparin), 5. Lavender/Pink (EDTA for hematology/CBC), 6. Gray (glycolytic inhibitor). Therefore, the light blue tube must be drawn first for the coagulation test, followed by the red tube for the serum chemistry panel, and finally the lavender tube for the CBC.
Question 2: Which of the following additives is correctly matched with its primary function in a blood collection tube?
- Sodium Fluoride - Clot activator
- EDTA - Anticoagulant that binds calcium (Correct answer)
- Heparin - Glycolysis inhibitor
- Thrombin - Anticoagulant that binds thrombin
Correct answer: EDTA - Anticoagulant that binds calcium
EDTA (Ethylenediaminetetraacetic acid) is an anticoagulant that works by chelating (binding) calcium ions, which are essential for the coagulation cascade, thus preventing the blood from clotting. Sodium fluoride is a glycolysis inhibitor, heparin is an anticoagulant that inhibits thrombin, and thrombin is a potent clot activator.
Question 3: A patient requires a blood draw for a Prothrombin Time (PT), a potassium level, and a blood alcohol level. The phlebotomist collects a light blue top tube, a green top tube, and a gray top tube. What is the consequence if the gray top tube is drawn before the green top tube?
- The PT result may be falsely shortened.
- The potassium level may be falsely elevated. (Correct answer)
- The blood alcohol level may be falsely decreased.
- The specimen in the green tube may become hemolyzed.
Correct answer: The potassium level may be falsely elevated.
The gray top tube contains potassium oxalate as an anticoagulant and sodium fluoride as a preservative. If the gray tube is drawn before the green tube (used for potassium level), the potassium oxalate can carry over and contaminate the green top tube, leading to a falsely elevated potassium result. The correct order is light blue, green, then gray.
Question 4: Why must blood culture tubes be drawn first in the order of draw?
- To prevent contamination of the culture with skin flora.
- To ensure the tube's vacuum is at its strongest.
- To prevent contamination of the culture with additives from other tubes. (Correct answer)
- To allow the anticoagulant in the culture media to work immediately.
Correct answer: To prevent contamination of the culture with additives from other tubes.
Blood culture tubes are drawn first to maintain the sterility of the sample and prevent contamination from additives in other tubes, which could inhibit bacterial growth and lead to false-negative results. While proper site cleaning is crucial to prevent skin flora contamination, the order of draw specifically addresses cross-contamination from other tubes.
Question 5: A phlebotomist uses a butterfly needle to collect only a light blue top tube for a coagulation study. Which of the following is a necessary step to ensure an accurate result?
- Invert the tube vigorously 15 times.
- Draw a discard tube before the light blue tube. (Correct answer)
- Slightly underfill the light blue tube.
- Warm the tube in an incubator before the draw.
Correct answer: Draw a discard tube before the light blue tube.
When using a butterfly collection set, the air in the tubing will displace blood, leading to an underfilled tube. Coagulation tubes (light blue) require a precise 9:1 ratio of blood to anticoagulant. Drawing a discard tube first purges the air from the tubing, ensuring the light blue tube fills to the correct volume.
Question 6: The additive in a green top tube is typically which of the following?
- Sodium Citrate
- Potassium Oxalate
- EDTA
- Lithium Heparin (Correct answer)
Correct answer: Lithium Heparin
Green top tubes contain either sodium heparin or lithium heparin as an anticoagulant. This additive works by inhibiting thrombin formation. Sodium citrate is found in light blue tubes, potassium oxalate in gray tubes, and EDTA in lavender or pink tubes.
Phlebotomy Order of Draw and Additives Questions and Answers 1
A phlebotomist needs to draw blood for a coagulation test, a complete blood count (CBC), and a serum chemistry panel.
Which of the following represents the correct order of draw?