Phlebotomy Technician Certification Exam
Order of Draw Practice Questions
60 practice questions with detailed explanations — aligned to the Phlebotomy Technician Certification Exam.
Master Order of Draw to boost your score on the Phlebotomy Technician Certification Exam. Each question below mirrors the style and difficulty of real exam questions, complete with detailed explanations so you understand the why behind every answer. Work through all 60 questions, review any that trip you up, and use the related topics below to round out your preparation.
Q1.According to CLSI guidelines, which of the following represents the correct order of draw for evacuated tubes?
A.Yellow, Blue, Red/Gold, Green, Lavender, GrayB.Blue, Yellow, Red/Gold, Green, Lavender, GrayC.Yellow, Red/Gold, Blue, Green, Lavender, GrayD.Red/Gold, Blue, Yellow, Lavender, Green, GrayA. Yellow, Blue, Red/Gold, Green, Lavender, GrayExplanation: The CLSI-recommended order of draw for evacuated tubes is: Yellow (SPS/blood culture), Blue (sodium citrate), Red or Gold (serum/SST), Green (heparin), Lavender (EDTA), Gray (fluoride/oxalate). This sequence prevents cross-contamination of additives between tubes.
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Q2.A lavender-top tube contains which anticoagulant?
A.Sodium citrateB.Lithium heparinC.EDTA (ethylenediaminetetraacetic acid)D.Sodium fluorideC. EDTA (ethylenediaminetetraacetic acid)Explanation: Lavender-top tubes contain EDTA (ethylenediaminetetraacetic acid), which chelates calcium ions to prevent clotting. EDTA tubes are the standard for complete blood count (CBC) and other hematology tests because they preserve cell morphology.
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Q3.Which tube is ALWAYS drawn first when collecting blood cultures?
A.Lavender-top tubeB.Yellow-top tube (blood culture bottle)C.Blue-top tubeD.Red-top tubeB. Yellow-top tube (blood culture bottle)Explanation: Blood culture bottles (yellow-top SPS tubes or aerobic/anaerobic bottles) are always collected first to minimize the risk of contamination from skin flora and to ensure the sample is not contaminated by additives from other tubes.
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Q4.A gray-top tube is PRIMARILY used for which laboratory test?
A.Complete blood count (CBC)B.Prothrombin time (PT)C.Glucose and blood alcohol levelsD.Serum electrolytesC. Glucose and blood alcohol levelsExplanation: Gray-top tubes contain sodium fluoride (a glycolytic inhibitor) and potassium oxalate (an anticoagulant). Sodium fluoride inhibits glycolysis and preserves glucose levels, making this tube the choice for glucose tolerance tests and blood alcohol specimens.
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Q5.Why must the blue-top (sodium citrate) tube be filled to the correct volume?
A.Underfilling will cause hemolysis of the sampleB.The citrate-to-blood ratio must be exactly 1:9 for accurate coagulation resultsC.Overfilling will activate platelets prematurelyD.The tube vacuum will collapse the vein if underfilledB. The citrate-to-blood ratio must be exactly 1:9 for accurate coagulation resultsExplanation: Sodium citrate tubes must maintain a precise 1:9 anticoagulant-to-blood ratio. An underfilled tube has excess citrate relative to the blood, which will artificially prolong PT and aPTT values. Overfilling introduces too much calcium-containing blood and can cause clotting.
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Q6.A gold-top or red/gray SST (serum separator tube) contains which additive?
A.EDTA and a clot activatorB.A thixotropic gel and a clot activatorC.Lithium heparin and a thixotropic gelD.Sodium citrate onlyB. A thixotropic gel and a clot activatorExplanation: Serum Separator Tubes (SST) contain a thixotropic gel that migrates between the clot and serum during centrifugation, and a clot activator (silica particles) to speed clot formation. After centrifugation, the gel barrier separates serum from the clot for chemistry testing.
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Q7.Which tube additive is used for lead and trace element testing to prevent contamination?
A.Standard EDTA lavender-topB.Royal blue-top tube with EDTA or no additiveC.Green-top lithium heparinD.Red-top with clot activatorB. Royal blue-top tube with EDTA or no additiveExplanation: Royal blue-top tubes are manufactured with special low-metal rubber stoppers and ultra-pure additives to prevent trace metal contamination. They are available with EDTA (for whole blood trace elements), with sodium heparin, or with no additive (for serum trace elements).
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Q8.When drawing from a butterfly (winged infusion set) with a blue-top tube as the first tube, what should the phlebotomist do?
A.Draw the blue-top tube directly without any preliminary stepB.Draw a small discard red or clear tube first to fill the tubing dead spaceC.Invert the blue tube 10 times immediately after collectionD.Apply extra pressure to the site after collectionB. Draw a small discard red or clear tube first to fill the tubing dead spaceExplanation: When using a butterfly set, the tubing contains air that will enter the tube first, underfilling the blue-top and altering the citrate-to-blood ratio. A small discard tube (red or clear) is collected first to fill the dead space of the tubing before collecting the blue-top tube.
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Q9.Green-top tubes contain which anticoagulant and are MOST commonly used for which tests?
A.EDTA; used for hematology panelsB.Sodium fluoride; used for glucose testingC.Heparin (lithium or sodium); used for plasma chemistry and stat electrolytesD.Sodium citrate; used for coagulation studiesC. Heparin (lithium or sodium); used for plasma chemistry and stat electrolytesExplanation: Green-top tubes contain heparin (lithium or sodium heparin), which inhibits thrombin and prevents clot formation. They are used for stat plasma chemistry tests and electrolyte panels because plasma can be obtained quickly without waiting for the clot to form.
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Q10.How many times should a lavender-top EDTA tube be gently inverted after collection?
A.0 times (do not mix)B.3–4 timesC.8–10 timesD.15–20 timesC. 8–10 timesExplanation: EDTA tubes should be gently inverted 8–10 times immediately after collection to ensure thorough mixing of blood with the anticoagulant and prevent microclot formation, which would interfere with CBC results. Vigorous shaking should be avoided to prevent hemolysis.
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