Phlebotomy Test Order of Draw and Additives 2 — Questions and Answers
Question 1: Which tube is collected FIRST in the venipuncture order of draw?
- EDTA lavender top
- Sodium citrate light blue top
- Blood culture bottles (Correct answer)
- Serum separator tube (SST)
Correct answer: Blood culture bottles
Blood culture bottles are always collected first to minimize contamination risk from skin flora.
Question 2: What additive is found in a royal blue top tube used for trace element testing?
- EDTA or no additive (K2EDTA or plain) (Correct answer)
- Sodium heparin
- Sodium citrate
- Lithium heparin
Correct answer: EDTA or no additive (K2EDTA or plain)
Royal blue tubes contain either EDTA or no additive and are made with trace-element-free stoppers to prevent contamination.
Question 3: A gray top tube contains which combination of additives?
- EDTA and aprotinin
- Sodium fluoride and potassium oxalate (Correct answer)
- Thrombin and silica
- Lithium heparin and gel separator
Correct answer: Sodium fluoride and potassium oxalate
Gray top tubes contain sodium fluoride (a glycolytic inhibitor) and potassium oxalate (an anticoagulant) for glucose testing.
Question 4: In the order of draw, where does the EDTA (lavender) tube fall relative to heparin tubes?
- After heparin tubes (Correct answer)
- Before heparin tubes
- At the same position
- Before light blue but after SST
Correct answer: After heparin tubes
EDTA tubes are drawn after heparin (green) tubes to prevent EDTA carryover from affecting coagulation or chemistry tests.
Question 5: Which tube additive works by binding calcium ions to prevent coagulation?
- Sodium fluoride
- Thrombin
- EDTA (Correct answer)
- Silica particles
Correct answer: EDTA
EDTA chelates (binds) calcium ions, which are essential for the coagulation cascade, thereby preventing clotting.
Question 6: A phlebotomist draws a light blue top tube and notices the tube did not fill completely. What is the main concern?
- Hemolysis will occur due to incomplete mixing
- The blood-to-additive ratio will be incorrect, affecting PT/INR results (Correct answer)
- The tube will clot before reaching the lab
- Glycolysis will continue in the underfilled tube
Correct answer: The blood-to-additive ratio will be incorrect, affecting PT/INR results
Light blue (sodium citrate) tubes require a precise 9:1 blood-to-anticoagulant ratio; underfilling alters this ratio and skews coagulation test results.
Question 7: Which color tube would be used when a physician orders a stat potassium level and the lab uses heparin plasma?
- Lavender (EDTA)
- Green (lithium heparin) (Correct answer)
- Red (no additive)
- Gray (sodium fluoride)
Correct answer: Green (lithium heparin)
Green top tubes with lithium heparin are used for plasma chemistry tests like potassium, providing faster results than serum tubes since no clotting is needed.
Phlebotomy Test Order of Draw and Additives 2
Which tube is collected FIRST in the venipuncture order of draw?