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22 Equipment & Order of Draw Practice Questions & Answers

Every Equipment & Order of Draw practice question from the Phlebotomy Technician Practice Test, with the correct answer and a short explanation.

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  1. 1. A requisition calls for a PT/INR, a chemistry panel in a gold gel tube, a CBC, and a fasting glucose. Following the CLSI order of draw, which tube is filled immediately after the light blue sodium citrate tube?

    • A.The gold serum separator tube, because serum tubes hold the position after citrate✓ Answer
    • B.The gray sodium fluoride tube, because its additive is the least likely to carry over
    • C.The lavender EDTA tube, because hematology samples are drawn before chemistry tubes
    • D.The green lithium heparin tube, because heparin tubes precede all other additives

    The CLSI venous sequence is blood culture/SPS, light blue citrate, serum tubes (plain red or gold/SST), heparin, EDTA, then sodium fluoride/oxalate. Serum tubes occupy the third position because a clot activator carried into a later tube does far less harm than heparin, EDTA or fluoride would.

    Source: CLSI GP41 (renumbered PRE02), venous order of drawReport a problem with this question

  2. 2. Under the CLSI order of draw, blood culture bottles or the yellow SPS tube are collected before every other tube. What is the reason for that position?

    • A.It protects the 9:1 ratio the culture bottle needs for reliable organism growth
    • B.It lets the largest volume be drawn while the vein is still fully dilated
    • C.It protects specimen sterility, since no additive can carry over into the culture✓ Answer
    • D.It keeps the SPS from chelating calcium and inhibiting the clotting sequence

    Cultures go first so the specimen stays sterile and no tube additive is carried into the bottle, either of which could mask or mimic growth. SPS is sodium polyanethol sulfonate, an anticoagulant that also inhibits complement and phagocytes; it is not a calcium chelator, and the 9:1 ratio belongs to the citrate tube.

    Source: CLSI GP41 (PRE02); NHA CPT Test PlanReport a problem with this question

  3. 3. A phlebotomist fills the lavender EDTA tube before the green heparin tube. The chemistry panel from the green tube is affected. Which pattern of error does the EDTA carryover produce?

    • A.Potassium and calcium are both falsely elevated above the true values
    • B.Potassium is falsely decreased and calcium is falsely elevated in that sample
    • C.Sodium is falsely elevated and glucose is falsely decreased in the sample
    • D.Potassium is falsely elevated and calcium is falsely decreased in the sample✓ Answer

    EDTA is supplied as a dipotassium or tripotassium salt, so carryover adds potassium to the next tube; at the same time EDTA chelates divalent cations, stripping calcium and magnesium from the sample. That is why EDTA sits near the end of the sequence, ahead of only the fluoride tube.

    Source: CLSI GP41 (PRE02) additive carryover rationaleReport a problem with this question

  4. 4. The gray sodium fluoride/potassium oxalate tube is placed last in the CLSI venous order of draw. Which statement explains that placement?

    • A.Its additive volume is the largest, so the tube needs the longest fill time
    • B.Its additives cause the most damaging carryover, so nothing may follow it✓ Answer
    • C.Its stopper is the least sterile, so it is kept away from culture bottles
    • D.Its glucose analyte is the most stable, so the tube can wait until the end

    Sodium fluoride inhibits the glycolytic enzymes and potassium oxalate distorts red cell morphology, so contamination of any later tube would corrupt both chemistry and hematology results. Placing the gray tube last means no tube can be spoiled by its carryover.

    Source: CLSI GP41 (PRE02) order of draw; NHA CPT Test PlanReport a problem with this question

  5. 5. A student draws the green heparin tube before the light blue citrate tube. How does the heparin carryover affect the coagulation results?

    • A.The aPTT is falsely prolonged, because heparin inhibits thrombin in the sample✓ Answer
    • B.The fibrinogen is falsely raised, because heparin stabilizes fibrin strands
    • C.The platelet count is falsely lowered, because heparin clumps the platelets
    • D.The aPTT is falsely shortened, because heparin activates the contact factors

    Heparin potentiates antithrombin and blocks thrombin, so even a trace carried into the citrate tube prolongs clot-based tests, especially the aPTT. This is why the citrate tube is drawn second, immediately after cultures and ahead of every other additive.

    Source: CLSI GP41 (PRE02); NHA CPT Test PlanReport a problem with this question

  6. 6. A winged collection set is used and the light blue citrate tube is the first tube to be drawn. What does the standard require for the discard tube?

    • A.A plain red tube is used and it must be filled to its full stated volume
    • B.A second citrate tube is used and it must reach the printed fill line
    • C.A lavender tube is used and it must be filled to at least half its volume
    • D.A nonadditive or coagulation tube is used and it need not be filled completely✓ Answer

    The discard tube exists only to displace the air sitting in the tubing dead space, so it must contain blood but does not have to be completely filled; it may be a nonadditive tube or another coagulation tube. If a blood culture or any other tube precedes the citrate tube, the tubing is already primed and no discard is needed.

    Source: CLSI GP41 (PRE02) winged-set discard tube guidanceReport a problem with this question

  7. 7. Two tubes on the tray have yellow stoppers. How do the yellow SPS tube and the yellow ACD tube differ in use?

    • A.SPS is used for coagulation, while ACD is used for glucose tolerance testing
    • B.SPS is used for blood cultures, while ACD is used for HLA and paternity testing✓ Answer
    • C.SPS is used for blood banking, while ACD is used for routine chemistry panels
    • D.SPS is used for trace metals, while ACD is used for therapeutic drug levels

    Stopper colour alone does not identify a tube: sodium polyanethol sulfonate is the microbiology anticoagulant that also inhibits complement and phagocytes, while acid citrate dextrose preserves cell viability for HLA typing, paternity and DNA studies. Only the SPS tube belongs in the blood culture position at the head of the order of draw.

    Source: CLSI GP41 (PRE02) tube additive tableReport a problem with this question

  8. 8. A physician orders a serum lithium level. Which collection choice is correct and why?

    • A.A lavender EDTA tube, because EDTA prevents the drug binding to platelets
    • B.A gray fluoride tube, because fluoride keeps the drug stable for 24 hours
    • C.A plain serum tube, because a lithium heparin tube would falsely raise the result✓ Answer
    • D.A lithium heparin tube, because its plasma gives the fastest turnaround time

    The anticoagulant salt becomes part of the specimen, so a lithium heparin tube adds measurable lithium and inflates the reported concentration. The same logic bars a sodium heparin tube for a sodium level and a gel tube for many therapeutic drug levels, because the drug can absorb into the gel.

    Source: CLSI GP41 (PRE02) additive-to-analyte interferenceReport a problem with this question

  9. 9. A royal blue trace element tube is included in a multi-tube draw. Where does it belong in the CLSI order of draw?

    • A.It is placed by its additive, so an EDTA version draws with the EDTA tubes✓ Answer
    • B.It is placed last of all, so the special stopper cannot shed trace metals
    • C.It is placed first of all, so no metal from other stoppers can contaminate it
    • D.It is placed after the citrate tube, so serum trace levels stay accurate

    Royal blue is a stopper made of low-trace-metal material, not a single additive, and the same colour is sold with no additive, with a clot activator, or with EDTA. Order of draw is governed by what is inside the tube, so the clot-activator version draws in the serum position and the EDTA version draws in the EDTA position.

    Source: CLSI GP41 (PRE02) placement of trace-element tubesReport a problem with this question

  10. 10. A light blue sodium citrate tube for a PT/aPTT is only two-thirds full. What is the effect on the result and the correct action?

    • A.The PT is prolonged but the aPTT is normal, so only the PT is recollected
    • B.The PT and aPTT are falsely shortened, so the specimen is rejected and redrawn
    • C.The PT and aPTT are falsely prolonged, so the specimen is rejected and redrawn✓ Answer
    • D.The PT and aPTT are unaffected, so the specimen is centrifuged and tested

    The citrate tube is designed for a fixed 9:1 blood-to-anticoagulant ratio. A short draw leaves relatively too much citrate, which binds the calcium added by the reagent and delays clot formation, so both clot-based times read long; the specimen cannot be corrected and must be recollected.

    Source: CLSI GP41 (PRE02) citrate fill volume and 9:1 ratio requirementReport a problem with this question

  11. 11. A phlebotomist compares a 21-gauge and a 23-gauge needle. Which statement about needle gauge is correct?

    • A.The two needles share a bore size, since gauge only states needle length
    • B.The 23-gauge needle has the smaller bore, since gauge rises as bore narrows✓ Answer
    • C.The 21-gauge needle has a thinner wall, since gauge states the wall thickness
    • D.The 23-gauge needle has the larger bore, since gauge rises as bore widens

    Gauge is an inverse convention: the higher the number, the narrower the lumen. That is why 21 gauge is the routine adult venipuncture size, 23 gauge is used with winged sets and hand veins, and the very large bores of 16 to 18 gauge are reserved for donation and therapeutic phlebotomy.

    Source: NHA CPT Test Plan, needle gauge sizes and lengthsReport a problem with this question

  12. 12. An elderly patient has fragile hand veins and needs a CBC and a chemistry panel. Which equipment choice best fits this draw?

    • A.An 18-gauge straight needle with a syringe, to shorten the collection time
    • B.A 25-gauge winged set with a large syringe, to reduce the vacuum pressure
    • C.A 23-gauge winged set with an evacuated tube holder and small-volume tubes✓ Answer
    • D.A 21-gauge straight needle with standard tubes, to keep the flow fastest

    A winged set with flexible tubing lets the needle be seated at a shallow angle in a small vein and held still, and 23 gauge is the standard bore for hand, pediatric and geriatric veins. Bores of 25 gauge are too narrow for venipuncture and hemolyze the sample, while 18 gauge is a donation size that would damage a fragile vessel.

    Source: NHA CPT Test Plan, device-selection considerationsReport a problem with this question

  13. 13. Blood collected in a syringe must be moved into evacuated tubes. Why is a safety transfer device used instead of pushing the blood through the needle into the stopper?

    • A.The tube fills faster this way, so clotting cannot begin before mixing occurs
    • B.The device adds anticoagulant, so the additive ratio stays correct in each tube
    • C.The tube draws its own volume, so cells are not sheared and no needle is exposed✓ Answer
    • D.The device filters small clots, so the tube stopper is not punctured twice

    Forcing blood through a fine needle shears red cells and causes hemolysis, and manual pressure over-fills or under-fills the tube so the blood-to-additive ratio is wrong. A transfer device lets each tube's own vacuum pull the correct volume while the needle stays enclosed, which also removes the needlestick hazard.

    Source: NHA CPT Test Plan, needle safety devices; CLSI GP41 (PRE02) syringe transferReport a problem with this question

  14. 14. A newly trained phlebotomist shakes each additive tube vigorously to mix it. What does this technique cause?

    • A.Fibrin strand formation that blocks the analyzer probe during serum sampling
    • B.Hemolysis and platelet activation, which invalidate potassium and platelet results✓ Answer
    • C.Foaming that pulls the additive out of solution and leaves the tube under-mixed
    • D.Additive layering at the stopper, which lowers the effective blood-to-additive ratio

    Shaking drives red cells against the tube wall and stopper hard enough to rupture their membranes, releasing intracellular potassium, LD and AST, and the same turbulence activates platelets. Correct mixing is a series of gentle complete inversions, each a full turn of the wrist and back.

    Source: CLSI GP41 (PRE02) mixing by inversion; NHA CPT Test PlanReport a problem with this question

  15. 15. A lavender EDTA tube is set on the tray and inverted only after the whole draw is finished. What is the most likely consequence?

    • A.The sample hemolyzes, so the potassium is falsely low and must be recollected
    • B.The EDTA settles out, so the red cell indices are falsely high on the analyzer
    • C.The serum separates early, so the smear shows an artificially thin cell layer
    • D.The blood microclots, so the platelet count is falsely low and it is rejected✓ Answer

    Spray-dried EDTA must reach the whole specimen before coagulation starts, which is within seconds of the blood entering the tube. Delayed inversion lets fibrin and platelet aggregates form, and those microclots consume platelets and make the count falsely low, so the specimen is rejected.

    Source: CLSI GP41 (PRE02) immediate mixing requirement for additive tubesReport a problem with this question

  16. 16. Several microcollection containers are filled from one fingerstick. Which sequence follows the CLSI capillary order of draw?

    • A.Blood gas tube, then serum tubes, then EDTA, then other additive tubes last
    • B.Blood gas tube, then EDTA, then other additive tubes, then serum tubes last✓ Answer
    • C.Serum tubes, then EDTA, then other additive tubes, then the blood gas tube last
    • D.EDTA, then blood gas tube, then serum tubes, then other additive tubes last

    The capillary sequence is essentially the reverse of the venous one: capillary blood gas first, then EDTA, then other additive containers, with serum containers last. Candidates who apply the venous order to a dermal puncture reliably get this wrong.

    Source: CLSI GP42, capillary order of drawReport a problem with this question

  17. 17. In a dermal puncture the EDTA microcollection container is filled before the serum container, the reverse of the venous order. What is the reason?

    • A.Serum containers hold more volume, so they are filled once flow is fastest
    • B.Hematology needs volume before platelets clump and the drops begin to clot✓ Answer
    • C.Serum tests need the longest clotting time, so that container is filled last
    • D.EDTA neutralizes the tissue fluid that contaminates the earliest drops of blood

    A dermal puncture produces a small wound that starts clotting immediately, and platelets aggregate at the puncture site within moments. Hematology results degrade fastest under those conditions, so the EDTA container is filled first to secure an adequate, clot-free volume for the cell count.

    Source: CLSI GP42, rationale for the capillary order of drawReport a problem with this question

  18. 18. A capillary specimen is needed from a 3-month-old infant. Which site and device are correct?

    • A.A heel lancet on the posterior curve at the back of the infant's heel
    • B.A heel lancet on the central arch of the sole, away from the bone
    • C.A heel lancet on the fleshy pad of the infant's middle finger instead
    • D.A heel lancet on the medial or lateral plantar surface of the heel✓ Answer

    Only the medial and lateral plantar surfaces of the heel lie far enough from the calcaneus that a depth-limited lancet cannot reach bone; puncturing the posterior curvature or the arch risks striking bone or nerves and can cause osteomyelitis. A finger stick is not used under one year of age because the tissue is too thin to protect the bone.

    Source: CLSI GP42, heel puncture site selection and depth limitationReport a problem with this question

  19. 19. Blood cultures are collected with a winged set directly into the bottles. Which bottle is inoculated first and why?

    • A.The anaerobic bottle, so the tubing air is expelled before the aerobic fills
    • B.The anaerobic bottle, so the strict anaerobes get the largest share of blood
    • C.The aerobic bottle, so the vacuum is checked before the anaerobic is filled
    • D.The aerobic bottle, so the air in the tubing does not enter the anaerobic one✓ Answer

    The tubing of a winged set holds a column of air that enters the first bottle inoculated. Filling the aerobic bottle first sends that air where oxygen does no harm; the order flips when a syringe is used, because there is no tubing air and the anaerobic bottle is filled first.

    Source: CLSI GP41 (PRE02) blood culture inoculation; NHA CPT Test PlanReport a problem with this question

  20. 20. Skin and bottle preparation for a blood culture on an adult uses which antiseptics?

    • A.Chlorhexidine on the skin and 70% alcohol on the bottle tops, both air-dried✓ Answer
    • B.Benzalkonium chloride on the skin and 70% alcohol on the bottle tops as well
    • C.70% alcohol on the skin and chlorhexidine on the bottle tops, both left to dry
    • D.Povidone-iodine on the skin and povidone-iodine on the bottle tops as well

    Chlorhexidine gluconate gives the sustained skin antisepsis needed to keep skin flora out of the bottle in patients over two months, and the bottle septum is wiped with 70% alcohol rather than iodine, which can degrade the septum. Both surfaces must air-dry, since a wet antiseptic is not yet working and can be carried into the specimen.

    Source: CLSI GP41 (PRE02) blood culture skin and bottle antisepsisReport a problem with this question

  21. 21. A legal blood alcohol specimen is ordered. Which antiseptic and tube combination is correct?

    • A.A non-alcohol antiseptic with a gray sodium fluoride tube kept capped✓ Answer
    • B.A 70% isopropyl alcohol prep with a red plain serum tube kept capped
    • C.A 70% isopropyl alcohol prep with a gray sodium fluoride tube kept capped
    • D.A non-alcohol antiseptic with a green lithium heparin tube kept capped

    An alcohol prep can contaminate the sample and gives the defense an argument that the reading is not the patient's own, so a non-alcohol antiseptic such as benzalkonium chloride or povidone-iodine is used. The gray tube is required because sodium fluoride stops microbial and cellular metabolism that would otherwise change the alcohol concentration, and the tube is not uncapped.

    Source: NHA CPT Test Plan, blood alcohol collection; CLSI GP41 (PRE02)Report a problem with this question

  22. 22. During equipment checks a phlebotomist finds a box of tubes past the printed expiration date. Why must they not be used?

    • A.The stopper colour has faded, so the tube can be matched to the wrong test
    • B.The gel barrier has hardened, so serum cannot be separated after spinning
    • C.The label adhesive has dried, so the patient label will not stay attached
    • D.The vacuum has degraded, so the tube under-fills and the additive ratio is wrong✓ Answer

    The expiration date marks how long the manufacturer guarantees both the vacuum and the additive, and a tube past that date draws a short, unreliable volume. The consequence is worst in ratio-dependent tubes such as citrate, where an under-filled draw prolongs the clotting times and forces a recollection.

    Source: NHA CPT Test Plan, equipment quality control checksReport a problem with this question

Concept-focused practice questions based on CLSI GP41 (venous blood collection), the CLSI order of draw, and the OSHA Bloodborne Pathogens Standard (29 CFR 1910.1030). Not affiliated with the NHA, ASCP, or CLSI, and not medical advice. Facility protocols and current CLSI standards take precedence — always follow your employer's procedures. About the CPT exam →