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Order of Draw and Additives Flashcards

7 cards from real Phlebotomy Test practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. A patient requires both a CBC and a prothrombin time (PT). In what order should the tubes be drawn?

    Answer: Light blue then lavender

    The light blue (sodium citrate) coagulation tube must be drawn before the lavender (EDTA) tube to prevent EDTA carryover that would chelate calcium and falsely prolong PT results.

  2. What is the primary function of thrombin as a tube additive?

    Answer: Rapidly accelerates clot formation for fast serum turnaround

    Thrombin-containing tubes (often clear or white top) rapidly clot blood within about 5 minutes, producing serum quickly for stat testing.

  3. Which of the following best describes why EDTA tubes come AFTER coagulation tubes in the order of draw?

    Answer: EDTA chelates calcium, which would inhibit the coagulation cascade in subsequent tests

    EDTA's calcium-chelating action would carry over into coagulation (citrate) tubes and falsely prolong clotting times if drawn first.

  4. A physician orders a lactic acid level. Which tube and special handling does this test require?

    Answer: Gray top (sodium fluoride/oxalate); transported on ice immediately

    Lactic acid tubes (gray top) contain sodium fluoride to stop glycolysis, and samples must be transported on ice to prevent continued lactate production.

  5. Potassium EDTA (K2EDTA) is preferred over sodium EDTA for hematology specimens because:

    Answer: Sodium EDTA causes red cell shrinkage while K2EDTA better preserves cell morphology

    K2EDTA is the CLSI-recommended anticoagulant for hematology because it preserves cell morphology and size better than sodium EDTA, which can cause red cell shrinkage.

  6. Which tube color is used for blood bank (type and screen, crossmatch) testing?

    Answer: Pink (EDTA)

    Pink top tubes contain EDTA and are specifically designated for blood bank testing to avoid confusion with other EDTA tubes, with special labeling requirements.

  7. If a phlebotomist accidentally draws a lavender tube before the light blue tube, what should be done?

    Answer: Discard both tubes and collect a fresh light blue tube with a new venipuncture

    EDTA contamination from the lavender tube invalidates the coagulation sample; both tubes should be discarded and recollected in the correct order.