CPHT Order of Draw & Tube Additives 1 — Questions and Answers
Question 1: What additive is found in a lavender/purple top collection tube?
- Sodium citrate
- EDTA (ethylenediaminetetraacetic acid) (Correct answer)
- Sodium heparin
- Sodium fluoride
Correct answer: EDTA (ethylenediaminetetraacetic acid)
Lavender/purple top tubes contain EDTA, an anticoagulant that chelates calcium to prevent clotting and preserve cell morphology for hematology testing.
Question 2: Which tube color is specifically used for coagulation studies such as PT/INR and aPTT?
- Green top (heparin)
- Red top (no additive)
- Light blue top (sodium citrate) (Correct answer)
- Gray top (fluoride/oxalate)
Correct answer: Light blue top (sodium citrate)
Light blue top tubes contain sodium citrate, which reversibly binds calcium to prevent clotting while allowing coagulation testing through calcium re-addition.
Question 3: What is the primary purpose of sodium fluoride in a gray top collection tube?
- Prevent clotting by chelating calcium
- Preserve cell morphology for differentials
- Inhibit glycolysis to preserve glucose levels (Correct answer)
- Promote rapid clot formation
Correct answer: Inhibit glycolysis to preserve glucose levels
Sodium fluoride inhibits the glycolytic enzyme enolase, stopping red blood cells from metabolizing glucose and preserving accurate glucose and lactate levels.
Question 4: Which anticoagulant is contained in a green top tube?
- EDTA
- Sodium citrate
- Heparin (Correct answer)
- Thrombin
Correct answer: Heparin
Green top tubes contain heparin (typically lithium heparin or sodium heparin), which enhances antithrombin III activity to prevent blood clotting.
Question 5: What does a gold top SST (Serum Separator Tube) contain?
- EDTA and gel separator
- Clot activator and gel separator (Correct answer)
- Heparin and gel separator
- Sodium citrate and gel separator
Correct answer: Clot activator and gel separator
Gold SST tubes contain silica particles as a clot activator and a polyester gel separator that migrates between serum and clot during centrifugation.
Question 6: Which tube color is specifically designated for blood bank (type and screen/crossmatch) testing?
- Lavender/purple EDTA tube
- Pink EDTA tube (Correct answer)
- Plain red tube (no additive)
- Yellow ACD tube
Correct answer: Pink EDTA tube
Pink top tubes contain EDTA and are specially designated for blood bank testing with strict labeling requirements to ensure patient safety during transfusion.
Question 7: Royal blue top tubes are primarily used for which type of testing?
- Routine blood cultures
- Trace elements and toxicology studies (Correct answer)
- Standard coagulation panels
- Routine blood typing
Correct answer: Trace elements and toxicology studies
Royal blue top tubes are constructed with low-contamination materials to prevent trace metal interference, making them essential for trace element, toxicology, and nutritional testing.
CPHT Order of Draw & Tube Additives 1
What additive is found in a lavender/purple top collection tube?