36 Routine Blood Collections Practice Questions & Answers

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. 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

8. 8. 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

9. 9. 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

10. 10. 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

11. 11. 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

12. 12. 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

13. 13. 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

14. 14. 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

15. 15. 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

16. 16. 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

17. 17. Immediately before entering the vein, how should the phlebotomist hold the skin and the needle?

    • A.Pinch the vein between the thumb and finger and enter bevel up at roughly 45 degrees
    • B.Anchor the skin above the site with a finger and enter bevel down at 15 to 30 degrees
    • C.Stretch the skin from both sides of the vein and enter bevel down at roughly 45 degrees
    • D.Anchor the skin below the site with the thumb and enter bevel up at 15 to 30 degrees✓ Answer

    Pulling the skin taut an inch or two below the site fixes the vein so it cannot roll and keeps the anchoring thumb behind the needle rather than in its path. A bevel-up entry at a shallow 15 to 30 degree angle lets the opening seat inside the lumen instead of shearing through the far wall.

    Source: CLSI GP41 venipuncture technique; NHA CPT Test PlanReport a problem with this question

18. 18. The last tube has filled. What is the correct order for the remaining steps?

    • A.Release the tourniquet, withdraw the needle, activate the safety device, then apply pressure✓ Answer
    • B.Activate the safety device, release the tourniquet, withdraw the needle, then apply pressure
    • C.Release the tourniquet, press on the site over the needle, withdraw it, then activate safety
    • D.Withdraw the needle, release the tourniquet, apply pressure, then activate the safety device

    The tourniquet comes off before the needle so that venous pressure is no longer raised when the vein is opened to the tissue, which is a leading cause of hematoma. The safety feature is engaged the instant the needle leaves the arm, and only then is pressure applied to the site with the arm held straight until bleeding stops.

    Source: CLSI GP41 completion of the venipuncture; NHA CPT Test PlanReport a problem with this question

19. 19. Blood runs into the first tube and then stops after a few milliliters. The needle has not moved and the vein still feels full. What should be tried first?

    • A.Seat a fresh tube on the holder, because the first tube may have lost vacuum✓ Answer
    • B.Remove the tourniquet completely and ask the patient to pump the fist hard
    • C.Withdraw the needle part way and redirect it sideways in search of the vein
    • D.Advance the needle through the far vein wall to reach a faster blood channel

    Flow that starts and then stops usually means that tube's vacuum is exhausted or was incomplete, so exchanging the tube is the first and least invasive check. Redirecting the needle sideways is lateral probing, which risks nerve injury, and vigorous fist pumping falsely raises the potassium result.

    Source: CLSI GP41 troubleshooting an unsuccessful draw; NHA CPT Test PlanReport a problem with this question

20. 20. Two venipuncture attempts on the same patient have both failed. What should the phlebotomist do next?

    • A.Try a third site on the opposite arm before involving any other staff member
    • B.Cancel the orders in the computer and ask the provider to reorder the tests
    • C.Collect the sample by capillary puncture and label it as a venous specimen
    • D.Stop and ask another phlebotomist or the patient's nurse to take over the draw✓ Answer

    Repeated punctures increase the risk of hematoma, nerve injury and patient distress, so after two unsuccessful attempts the collection is handed to a second collector rather than continued. Relabeling a capillary sample as venous falsifies the record, and canceling a provider's orders is outside the phlebotomist's scope.

    Source: CLSI GP41 limits on repeat attempts; NHA CPT Test PlanReport a problem with this question

21. 21. As the needle is advanced, the patient reports a sharp electric pain shooting into the thumb, with tingling. What should the phlebotomist do first?

    • A.Discontinue the draw at once, withdraw the needle, and report the event✓ Answer
    • B.Reposition the needle slightly and go on if the pain begins to settle
    • C.Loosen the tourniquet and fill the tube quickly to shorten the discomfort
    • D.Finish the collection and then apply a cold compress to the arm afterward

    Shooting or electric pain with tingling or numbness suggests the needle has struck or is irritating a nerve, and continuing or repositioning can turn a transient injury into a lasting one. The needle is withdrawn immediately and the incident is reported and documented, since nerve injury is a reportable complication.

    Source: CLSI GP41 nerve injury during venipuncture; NHA CPT Test PlanReport a problem with this question

22. 22. Bright red blood pulses into the tube and fills it unusually fast. What is the correct action?

    • A.Keep the needle in place and slow the flow by loosening the tourniquet a little
    • B.Finish the tubes, bandage the arm and note the rapid fill on the requisition
    • C.Remove the needle and hold firm pressure for at least five minutes, then report✓ Answer
    • D.Remove the needle and let the patient hold a light dressing over the site alone

    Bright red pulsating blood that fills a tube very quickly indicates an artery has been entered, and arterial pressure will produce a large hematoma unless the site is compressed hard for at least five minutes. The needle comes out immediately, a supervisor is notified, and the specimen is identified as arterial because some results differ from venous blood.

    Source: CLSI GP41 accidental arterial puncture; NHA CPT Test PlanReport a problem with this question

23. 23. A swelling rises quickly under the skin at the puncture site while the second tube is filling. What should the phlebotomist do first?

    • A.Withdraw the needle and rub the site briskly to spread the pooled blood out
    • B.Release the tourniquet, withdraw the needle and press firmly over the site✓ Answer
    • C.Leave the needle in and press above the site until the swelling stops growing
    • D.Finish the tube quickly, then apply a warm compress to disperse the swelling

    A swelling that appears during the draw is blood leaking into the tissue, usually because the bevel is only partly in the lumen or has passed through the far wall, and continuing enlarges the hematoma. The tourniquet is released, the needle removed and firm direct pressure applied; a cold pack afterward limits swelling, while heat or rubbing increases bleeding.

    Source: CLSI GP41 hematoma formation; NHA CPT Test PlanReport a problem with this question

24. 24. Midway through the collection the patient turns pale and sweaty and says the room is spinning. What should the phlebotomist do first?

    • A.Hold an ammonia inhalant under the nose and finish the remaining tube fast
    • B.Stop the draw, remove the needle and lower the head, staying with the patient✓ Answer
    • C.Leave to find help and let the patient rest quietly in the chair meanwhile
    • D.Ask the patient to sit up straighter and keep talking while the draw goes on

    Pallor, sweating and dizziness are the warning signs of syncope, and a patient who faints with a needle in the arm can be injured, so the needle comes out first. The head is lowered between the knees or the patient is laid flat and never left alone; ammonia inhalants are no longer used because they can provoke bronchospasm in asthmatic patients.

    Source: NHA CPT Test Plan, first aid; CLSI GP41 adverse patient reactionsReport a problem with this question

25. 25. Small flat red pinpoint spots appear on the forearm below the tourniquet. What does this most likely indicate?

    • A.A capillary or platelet defect, so prolonged bleeding at the site is likely✓ Answer
    • B.A hematoma is already forming, so the specimen must be discarded and redrawn
    • C.The tourniquet is too loose, so the vein will collapse once the flow starts
    • D.An allergy to the tourniquet material, so the bleeding time will be normal

    Petechiae are tiny capillary hemorrhages and point to a platelet or capillary fragility problem in the patient rather than to a technique error. They are not by themselves a reason to cancel the collection, but they warn the phlebotomist that the site is likely to bleed longer than usual and that pressure must be held accordingly.

    Source: NHA CPT Test Plan, complications; CLSI GP41 patient assessmentReport a problem with this question

26. 26. A patient taking warfarin is still bleeding at the site after the usual period of pressure. What should the phlebotomist do first?

    • A.Clean the site with alcohol again and cover it with a fresh adhesive bandage
    • B.Keep applying direct pressure with the arm raised and notify the nurse if it goes on✓ Answer
    • C.Wrap the arm tightly in a pressure bandage and send the patient on their way
    • D.Place a cotton ball and have the patient bend the elbow firmly for five minutes

    Anticoagulants prolong bleeding, so the first response is continued direct pressure over the site with the arm elevated, and the nurse or provider is informed if bleeding does not stop within about five minutes. Bending the elbow instead of pressing on the site is a classic cause of hematoma, and a tight wrap conceals continued bleeding rather than controlling it.

    Source: NHA CPT Test Plan, post-puncture care; CLSI GP41Report a problem with this question

27. 27. A patient says that adhesive bandages leave an itchy raised rash on the skin. What is the best action?

    • A.Put an antihistamine cream on the site before covering it with the usual bandage
    • B.Place the adhesive bandage over folded gauze so the tape never touches the skin
    • C.Apply the usual adhesive bandage and tell the patient to take it off in an hour
    • D.Hold gauze in place with a self-adhering wrap or paper tape instead of a bandage✓ Answer

    A reported adhesive sensitivity is respected by choosing a different dressing, such as gauze secured with a self-adhering wrap or paper tape, and the reaction is noted in the patient's record. Applying any medication is outside the phlebotomist's scope of practice, and the edges of the tape still contact skin even when the gauze pad underneath is enlarged.

    Source: NHA CPT Test Plan, post-puncture care and allergy assessmentReport a problem with this question

28. 28. A phlebotomist prepares to apply a tourniquet for a routine venipuncture in the antecubital area. Where should the tourniquet be placed, and how long may it remain on before the draw begins?

    • A.3-4 inches below the site, for no more than 5 minutes
    • B.3-4 inches above the site, for no more than 1 minute✓ Answer
    • C.1-2 inches above the site, for no more than 3 minutes
    • D.6-8 inches above the site, for no more than 2 minutes

    The tourniquet goes 3-4 inches above the intended site — close enough to distend the vein without contaminating the cleansed area. It must not stay on longer than 1 minute because prolonged stasis causes hemoconcentration, falsely elevating potassium, proteins, and cell counts; if the vein search runs long, release it and reapply after about 2 minutes.

    Source: CLSI GP41 (venipuncture standard); NHA CPT Test Plan Domain 3, Task 3E / k60 — tourniquet 3-4 in above site, ≤1 minuteReport a problem with this question

29. 29. While the tourniquet is on, a patient repeatedly clenches and opens the fist to "help the blood flow." Why must the phlebotomist ask the patient to stop pumping?

    • A.Pumping dilutes the specimen with muscle tissue fluid
    • B.Pumping makes the vein roll away from the needle path
    • C.Pumping raises blood pressure and causes arterial bleeding
    • D.Pumping falsely raises potassium and lactate levels✓ Answer

    Repeated muscle contraction releases potassium and lactate from the forearm muscle cells into the blood, so pumping the fist falsely elevates those results. The patient may make and hold a gentle fist, but must not pump it; vein rolling, arterial bleeding, and tissue-fluid dilution are not effects of fist pumping.

    Source: CLSI GP41; NHA CPT Test Plan k60 — fist pumping falsely elevates potassium and lactateReport a problem with this question

30. 30. After cleansing the venipuncture site with 70% isopropyl alcohol, what should the phlebotomist do just before inserting the needle?

    • A.Let the site air-dry completely, about 30 seconds✓ Answer
    • B.Blow gently on the site to evaporate the alcohol
    • C.Blot the site dry using a clean, dry gauze pad
    • D.Fan the site with a gloved hand to dry it faster

    The alcohol must be allowed to air-dry (about 30 seconds) because drying time is part of its antiseptic action, and residual wet alcohol causes stinging on puncture and can hemolyze the specimen. Fanning, blowing, or wiping the site recontaminates the cleansed skin and defeats the antisepsis.

    Source: CLSI GP41 — site antisepsis: allow 70% isopropyl alcohol to air-dry; do not fan, blow on, or re-touch the siteReport a problem with this question

31. 31. During an evacuated tube draw, the phlebotomist keeps the patient's arm angled downward so each tube fills from the bottom up with the stopper uppermost. What does this positioning prevent?

    • A.Loss of tube vacuum before the tube fills completely
    • B.Foaming of the blood as it enters the empty tube
    • C.Pressure of the needle bevel against the vein wall
    • D.Backflow of tube additives into the patient's vein✓ Answer

    With the arm downward and the stopper up, blood in the tube stays away from the needle end, so tube contents cannot flow back through the needle into the circulation. This prevents reflux of additives such as EDTA into the patient — which can cause adverse reactions — and also reduces additive carryover between tubes.

    Source: CLSI GP41 — arm positioned downward, tube stopper up, to prevent reflux/backflow of tube contents into the veinReport a problem with this question

32. 32. While assembling equipment, a phlebotomist notices that the only lavender EDTA tubes on the tray expired last month. What is the correct action?

    • A.Reserve them only for tests that do not require an additive
    • B.Discard them and obtain in-date tubes before drawing✓ Answer
    • C.Use them as long as the vacuum still pulls a full draw
    • D.Keep them but write the expiration date on each label

    Expired tubes must never be used because their vacuum weakens over time — causing short draws and a wrong blood-to-additive ratio — and the additive itself degrades, so results become unreliable. Checking expiration dates and tube integrity is part of required equipment quality verification before every draw.

    Source: NHA CPT Test Plan k56/k58 (equipment quality verification); CLSI GP41 and tube manufacturer instructions — do not use expired evacuated tubesReport a problem with this question

33. 33. No veins are visible or palpable in the antecubital area of a patient with obesity. Which approach is most likely to locate a suitable vein?

    • A.Tighten the tourniquet much harder to make a vein rise
    • B.Rotate the arm slightly and palpate for the cephalic vein✓ Answer
    • C.Probe the basilic area, where the deep veins are safest
    • D.Switch to a fingerstick to collect all the ordered tests

    In patients with obesity the cephalic vein, on the lateral (thumb) side, is often the most accessible and can frequently be felt after rotating the arm slightly; palpation, not sight, locates it. The basilic side lies near the brachial artery and median nerve and is never probed, a fingerstick cannot supply most venous test volumes, and over-tightening the tourniquet causes hemoconcentration and can block arterial flow.

    Source: NHA CPT Test Plan k55/k61 (equipment and site adaptation); Phlebotomy Essentials (McCall) — cephalic vein most accessible in obese patients, locate by rotating the armReport a problem with this question

34. 34. A 4-year-old child needs several tests, and the analyzer accepts reduced sample volumes. Why are pediatric partial-draw tubes preferred over regular adult tubes filled only partway?

    • A.They can be topped off later from a second venipuncture
    • B.They contain no additives, so the fill volume does not matter
    • C.They keep the blood-to-additive ratio correct at low volume✓ Answer
    • D.Their stronger vacuum pulls blood faster from small veins

    Partial-draw (pediatric or short-draw) tubes have a reduced vacuum matched to a smaller additive amount, so the tube stops filling at exactly the volume that keeps the blood-to-additive ratio correct. Filling a regular adult tube only partway leaves excess additive relative to blood, which distorts results, and tubes must never be topped off from a later draw.

    Source: CLSI GP41; NHA CPT Test Plan Task 3D / k58 — minimum-volume (partial-draw) tubes preserve the required blood-to-additive ratioReport a problem with this question

35. 35. Before a fingerstick, the phlebotomist applies a warming device to increase blood flow to the site. Which time and temperature limits are correct?

    • A.Warm for 15 minutes at no more than 37 °C
    • B.Warm for 8-10 minutes at no more than 45 °C
    • C.Warm for 1-2 minutes at no more than 50 °C
    • D.Warm for 3-5 minutes at no more than 42 °C✓ Answer

    Warming the site for 3-5 minutes at no more than 42 °C increases capillary blood flow up to sevenfold — 'arterializing' the specimen — without injuring the skin. Temperatures above 42 °C can burn the patient, which is why commercial heel and finger warmers are engineered not to exceed that limit.

    Source: CLSI GP42 (capillary blood specimens) — warm site 3-5 minutes at a temperature not exceeding 42 °CReport a problem with this question

36. 36. During a fingerstick, blood flows slowly, so a phlebotomist squeezes the finger hard and collects the very first drop that forms. What should have been done instead?

    • A.Wipe away the first drop and apply gentle, intermittent pressure✓ Answer
    • B.Wipe away the first drop and milk the finger from base to tip
    • C.Collect the first drop while keeping firm, steady finger pressure
    • D.Collect every drop while squeezing and warming the fingertip

    The first drop is wiped away because it contains excess tissue fluid (and any alcohol residue) that dilutes the specimen and can activate clotting. Flow is then encouraged with gentle, intermittent pressure and a downward hand position; strong squeezing or 'milking' hemolyzes cells and forces in more tissue fluid, invalidating results.

    Source: CLSI GP42 — wipe away the first drop of capillary blood; do not squeeze or milk the puncture siteReport 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 →