22 Equipment & Order of Draw Practice Questions & Answers

1. 1. CLSI PRE02 (formerly GP41) publishes the venipuncture order of draw as six additive categories rather than nine stopper colors. Which category is collected fourth?

   • A.Sodium citrate (light blue)
   • B.EDTA (lavender, pink, pearl/white)
   • C.Glycolytic inhibitor: sodium fluoride/potassium oxalate (gray)
   • D.Heparin, with or without gel (dark green, light green, speckled green)✓ Answer

   The six CLSI steps are (1) sterile blood culture, (2) sodium citrate, (3) serum with or without clot activator and/or gel, (4) heparin, (5) EDTA, (6) glycolytic inhibitor. Heparin sits fourth because it must follow the serum tubes (heparin carryover interferes with clot-based testing) yet must precede EDTA, whose potassium-rich, calcium-chelating carryover would corrupt the chemistry analytes measured in the heparin and serum tubes.

   Source: CLSI PRE02-Ed8 (2025), venous order of draw, step 4 of 6 (document formerly numbered GP41-Ed7)Report a problem with this question

2. 2. A patient has orders for blood cultures, a type and screen (pink K2EDTA), a PT/INR (light blue), a comprehensive metabolic panel (gold SST), and a fasting glucose (gray). Using an evacuated tube system, which tube is collected third?

   • A.The gold SST✓ Answer
   • B.The pink K2EDTA tube
   • C.The gray sodium fluoride/potassium oxalate tube
   • D.The light blue sodium citrate tube

   The sequence here is blood culture (1st), light blue citrate (2nd), gold serum (3rd), pink (4th), gray (5th). The pink tube is positioned by its additive — K2EDTA — not by its color, so it belongs to the EDTA category (CLSI step 5), after all serum and heparin tubes; its pink stopper only signals an AABB-compliant blood bank label. That leaves the gold SST third.

   Source: CLSI PRE02-Ed8 order of draw; rule that stopper colors not named in the six steps are placed by their additive (K2EDTA = EDTA category)Report a problem with this question

3. 3. Why does CLSI place blood culture bottles and tubes in the first position of the order of draw?

   • A.Contact with non-sterile tube stoppers can transfer organisms to the needle and cause false-positive cultures✓ Answer
   • B.Culture bottles require more vacuum than any other collection container
   • C.The SPS additive would be diluted by blood if the bottles were filled later
   • D.Blood culture bottles contain no additive, so nothing can carry over from them

   Blood cultures are drawn first to protect sterility: once the needle has pierced a non-sterile rubber stopper, organisms from that stopper can be introduced into the culture bottle, generating a false-positive result that may trigger unnecessary antibiotics and prolonged admission. The same sterile-first logic applies to the yellow SPS tube, which occupies this position when bottles are not used.

   Source: CLSI PRE02-Ed8, order of draw step 1 (sterile blood culture tube/bottle first)Report a problem with this question

4. 4. A phlebotomist collects the lavender EDTA tube before the green heparin tube. Which pattern of erroneous results should be expected on the chemistry panel?

   • A.Falsely increased potassium with falsely decreased calcium and alkaline phosphatase✓ Answer
   • B.No analytic effect, because EDTA does not interfere with chemistry testing
   • C.Falsely increased calcium with falsely increased alkaline phosphatase
   • D.Falsely decreased potassium with falsely increased calcium

   EDTA is supplied as a potassium salt (K2EDTA or K3EDTA), so even a trace carried on the back of the needle adds potassium to the next tube and falsely raises the result. EDTA also irreversibly chelates calcium, so it strips calcium from the specimen — lowering measured calcium and depressing alkaline phosphatase, a metal-dependent enzyme. This is precisely why every serum and heparin tube is drawn before EDTA tubes.

   Source: CLSI PRE02-Ed8, rationale for order of draw: EDTA additive carryover (potassium salt; calcium chelation)Report a problem with this question

5. 5. What is the rationale for collecting the gray sodium fluoride/potassium oxalate tube after the lavender EDTA tube?

   • A.Gray tubes carry more vacuum and would collapse the vein if drawn first
   • B.Fluoride would neutralize the EDTA and allow the specimen to clot
   • C.Glucose degrades if the gray tube is drawn early in the sequence
   • D.Fluoride/oxalate carryover distorts cell morphology and hemolyzes red cells, invalidating the CBC and differential✓ Answer

   Potassium oxalate distorts red and white cell morphology and, together with fluoride, causes hemolysis, so any carryover into a hematology specimen would make the WBC differential unreadable and the CBC unreliable. Fluoride also inhibits enzymes and falsely lowers many chemistry analytes, which is why the gray tube is the final step of the CLSI sequence.

   Source: CLSI PRE02-Ed8, order of draw step 6 (glycolytic inhibitor last); oxalate/fluoride carryover effect on cell morphologyReport a problem with this question

6. 6. According to CLSI, which tube types may be collected BEFORE the light blue sodium citrate tube?

   • A.A blood culture tube/bottle, a glass non-additive serum tube, or a plastic serum tube without clot activator✓ Answer
   • B.Any red-top tube, whether glass or plastic
   • C.A gold-top serum separator tube
   • D.A green lithium heparin tube

   Clot activator carried over into a citrate tube starts the clotting cascade prematurely and falsely SHORTENS the PT and aPTT, so CLSI permits only sterile culture containers and serum tubes that contain no clot activator to precede the coagulation tube. Note that most modern plastic red tops DO contain a silica clot activator and therefore may not precede a light blue tube.

   Source: CLSI PRE02-Ed8, order of draw step 2 note: only blood culture tubes, glass non-additive serum tubes, or plastic serum tubes without clot activator may precede the citrate tubeReport a problem with this question

7. 7. A winged (butterfly) collection set is used, and the only tube ordered is a light blue sodium citrate tube for a PT/INR. What should the phlebotomist do?

   • A.Draw a discard tube first to displace the air in the tubing; the discard tube need not be completely filled✓ Answer
   • B.Fill the citrate tube to only half of the fill line to compensate for the tubing
   • C.Draw a lavender EDTA tube first and discard it
   • D.Draw nothing first, because winged set tubing contains no dead space

   The tubing of a winged set holds air (dead space). If the citrate tube is the first tube, that air is pulled into it and consumes part of the tube's preset vacuum, so the tube underfills and the 9:1 blood-to-citrate ratio is lost. A discard tube purges the air; because its only job is to displace dead space, it does not have to fill completely.

   Source: CLSI PRE02-Ed8: discard tube required when a citrate tube is the first tube drawn through a winged blood collection set (tubing dead space / 9:1 ratio)Report a problem with this question

8. 8. Which tube is acceptable to use as the discard tube before a citrate tube collected through a winged set?

   • A.A non-additive tube or another sodium citrate tube✓ Answer
   • B.A plastic red-top tube, because red tops are drawn early in the order
   • C.A gold-top SST, because the gel keeps the additive away from the needle
   • D.A green heparin tube, because heparin does not affect the PT/INR

   The discard tube must contribute nothing that could alter the coagulation result, so it must be a true non-additive tube or another citrate tube. Modern plastic red tops contain a silica clot activator whose carryover would shorten the PT and aPTT, and heparin is a direct anticoagulant that would prolong clot-based testing — neither is an acceptable discard tube.

   Source: CLSI PRE02-Ed8: discard tube must be a non-additive or citrate tube (plastic red-top tubes contain clot activator)Report a problem with this question

9. 9. A light blue sodium citrate tube stops filling at about two-thirds of the fill line. What is the correct action, and why?

   • A.Top it off from a second citrate tube, then send it
   • B.Recollect, because underfilling falsely shortens the PT and aPTT
   • C.Send the tube; fill volume does not affect clot-based coagulation testing
   • D.Recollect in a new citrate tube, because excess citrate binds reagent calcium and falsely prolongs the PT and aPTT✓ Answer

   Citrate tubes are manufactured for an exact 9:1 blood-to-anticoagulant ratio. When the tube is underfilled, the fixed volume of citrate is in relative excess and continues to bind the calcium added by the testing reagent, delaying clot formation and falsely PROLONGING the PT and aPTT. The specimen must be recollected; topping off from another tube is never acceptable because it double-anticoagulates and partially activates the added blood.

   Source: CLSI PRE02-Ed8: sodium citrate tubes require a 9:1 blood-to-anticoagulant ratio; underfilled coagulation tubes are rejected and recollectedReport a problem with this question

10. 10. Which statement about needle gauge is correct?

    • A.The higher the gauge number, the larger the bore; 16-18 G is standard for routine adult venipuncture
    • B.Gauge and bore size are unrelated; 25 G is standard for routine adult venipuncture
    • C.Gauge describes the needle's length, not the size of its bore
    • D.The higher the gauge number, the smaller the bore; 21 G is standard for routine adult venipuncture✓ Answer

    Gauge is inversely related to bore diameter: a larger number means a narrower needle. A 21 G needle is the routine adult default, 22 G is chosen for small or fragile veins, and 23 G is typically used as a winged set for hand veins and small children; 16-18 G needles are reserved for donation and apheresis, where high flow is required. Bores narrower than 23 G force red cells through a tight lumen and cause hemolysis as well as very slow flow.

    Source: CLSI PRE02-Ed8, needle selection: gauge is inversely proportional to bore; 21 G routine adult venipunctureReport a problem with this question

11. 11. Which situation is the most appropriate indication for a 23 G winged infusion (butterfly) set?

    • A.A whole-blood donation collection
    • B.A routine adult antecubital draw of six tubes
    • C.A small, shallow hand vein in an older adult or a young child✓ Answer
    • D.A large-volume therapeutic phlebotomy

    A winged set pairs a short, small-bore needle with flexible tubing, so it can be seated at a shallow angle in a small superficial vein and stays stable when the vein cannot tolerate the leverage of a rigid tube holder. Routine antecubital draws are better served by a 21 G evacuated tube system, and donation and therapeutic phlebotomy need the high flow of a 16-18 G needle. Remember that whenever a citrate tube is drawn first through a winged set, a discard tube is required.

    Source: CLSI PRE02-Ed8, collection device selection: winged blood collection sets for small, shallow, or hand veinsReport a problem with this question

12. 12. Blood has been collected into a syringe from a fragile vein that would collapse under evacuated-tube vacuum. How should the blood be placed into the tubes?

    • A.With a safety transfer device, filling the tubes in the standard order of draw✓ Answer
    • B.By pushing the syringe needle through each stopper and depressing the plunger
    • C.By removing the stoppers and pouring the blood in, in any order
    • D.In any order, because the order of draw applies only to evacuated tube systems

    CLSI applies the same order of draw to evacuated tube holders, syringes, and winged sets, because additive carryover between tubes happens regardless of the device. A safety transfer device lets each tube fill under its own vacuum, which preserves the correct fill volume and additive ratio; pushing blood through a stopper with the needle risks needlestick injury, hemolysis from pressure, and overfilling.

    Source: CLSI PRE02-Ed8: the order of draw applies to evacuated tube holders, syringes, and winged sets alike; syringe-to-tube transfer requires a safety transfer deviceReport a problem with this question

13. 13. Immediately after collection, how should a light blue sodium citrate tube be mixed?

    • A.With 3 to 4 gentle inversions, one inversion being a 180-degree turn and back✓ Answer
    • B.With 8 gentle inversions, one inversion being a 180-degree turn and back
    • C.With 8 to 10 vigorous shakes
    • D.Not at all; liquid citrate mixes on its own

    Citrate tubes require only 3 to 4 gentle inversions, and one inversion is defined as turning the tube 180 degrees and back. Mixing must be immediate so the anticoagulant contacts all the blood before microclots form, and it must be gentle — shaking hemolyzes red cells. For comparison, blood culture, heparin, EDTA, and gray tubes take 8 inversions, plastic red and gold tubes take 5, and a glass non-additive red tube takes none.

    Source: CLSI PRE02-Ed8 / manufacturer mixing guidance: sodium citrate tubes, 3-4 gentle inversions immediately after collectionReport a problem with this question

14. 14. What is the consequence of shaking an additive tube instead of gently inverting it?

    • A.Falsely decreased potassium from dilution of the additive
    • B.Loss of the tube's residual vacuum
    • C.Microclot formation from inadequate contact between blood and additive
    • D.Hemolysis and platelet activation, which falsely elevate potassium, LDH, and AST✓ Answer

    Vigorous shaking generates shear forces that rupture red cell membranes and activate platelets. Because potassium, LDH, and AST are far more concentrated inside red cells than in plasma, the released intracellular contents falsely elevate those results — along with magnesium, phosphorus, and free hemoglobin. Under-mixing produces the opposite problem, microclots, which is why the technique is gentle inversion rather than either extreme.

    Source: CLSI PRE02-Ed8, specimen mixing: gentle inversion required; shaking causes hemolysis (hemolysis falsely elevates K, LDH, AST)Report a problem with this question

15. 15. A lavender EDTA tube is set down and is not inverted until several minutes after collection. Hematology reports microclots in the specimen. Why is the specimen unacceptable?

    • A.Additional EDTA can be added to dissolve the clot before testing
    • B.Microclots do not affect cell counts, so the tube may be run as-is
    • C.The clot affects only the glucose result
    • D.Clot formation consumes platelets and cells, producing falsely low CBC counts, so the specimen must be recollected✓ Answer

    EDTA works only where it contacts blood, so delayed mixing lets clotting begin. Platelets and leukocytes are trapped in the fibrin mesh and are no longer available to be counted, giving falsely low platelet and cell counts, and clots can also obstruct the analyzer. Clotting is irreversible — EDTA chelates calcium to prevent clots but cannot dissolve one — so the only remedy is recollection.

    Source: CLSI PRE02-Ed8: additive tubes must be inverted immediately after collection; clotted EDTA specimens are rejected for CBCReport a problem with this question

16. 16. In capillary (dermal puncture) collection under CLSI GP42, which specimen is filled first among the routine micro-collection containers, and why?

    • A.Gray fluoride/oxalate, so that glucose is preserved before it is metabolized
    • B.Lavender EDTA, because skin puncture activates platelets immediately and clumping would falsely lower the platelet count✓ Answer
    • C.Green lithium heparin, because plasma specimens are the most fragile
    • D.Serum (red/gold), because clotting should be allowed to begin first

    The capillary order is essentially the reverse of the venipuncture order: blood gas first if collected, then the lavender EDTA micro-collection container, then other additive tubes (green, gray), and serum tubes last. The reason is mechanical, not chemical — the skin puncture itself activates platelets at the site immediately, so the hematology specimen must be obtained before clumping makes the platelet count falsely low. This sequence comes from CLSI GP42, not PRE02.

    Source: CLSI GP42-Ed7 (2020), capillary order of draw: blood gas, then EDTA, then other additive tubes, serum lastReport a problem with this question

17. 17. Which option describes the correct site and maximum depth for an infant heelstick?

    • A.The medial or lateral plantar surface of the heel, to a depth no greater than 2.0 mm✓ Answer
    • B.The pad of the great toe, to a depth no greater than 2.0 mm
    • C.The medial or lateral plantar surface of the heel, to a depth no greater than 5.0 mm
    • D.The central plantar arch of the heel, to a depth no greater than 2.0 mm

    Only the medial and lateral plantar surfaces of the heel have enough soft tissue between skin and the calcaneus, and the depth is limited to 2.0 mm so the lancet cannot reach bone and cause osteomyelitis. The central heel and the arch are avoided because nerves, tendons, and bone lie close to the surface there, previous puncture sites are avoided because of infection risk, and fingers are not used in infants under 1 year. The first drop is wiped away because it is diluted with tissue fluid.

    Source: CLSI GP42-Ed7 (2020), dermal puncture site selection: medial/lateral plantar heel surface, puncture depth not to exceed 2.0 mm in infantsReport a problem with this question

18. 18. A tourniquet is left in place for three minutes while the phlebotomist searches for a vein. Which effect on results should be anticipated?

    • A.Falsely decreased potassium and lactate
    • B.Hemodilution, falsely lowering total protein and cell counts
    • C.Hemoconcentration, falsely elevating potassium, calcium, total protein, and cell counts✓ Answer
    • D.No analytic effect, since the tourniquet is released before the tubes fill

    Prolonged venous stasis forces water and small molecules out of the vessel while protein-bound analytes and cells stay behind, concentrating them locally. The result is falsely elevated potassium, calcium, total protein, albumin, cholesterol, iron, lactate, and cell counts, plus hemolysis. The tourniquet must not remain on longer than 1 minute; if more time is needed to locate a vein, release it and reapply after 2 minutes. Fist pumping is prohibited for the same reason, since muscle contraction releases potassium and lactate.

    Source: CLSI PRE02-Ed8, tourniquet application: maximum 1 minute before venipuncture; reapply after 2 minutes (hemoconcentration)Report a problem with this question

19. 19. A legally defensible blood alcohol specimen is ordered. Which combination of site preparation and collection tube is correct?

    • A.Aqueous benzalkonium chloride or povidone-iodine prep; gray sodium fluoride/potassium oxalate tube✓ Answer
    • B.70% isopropyl alcohol prep; lavender K2EDTA tube
    • C.Chlorhexidine gluconate prep; light blue sodium citrate tube
    • D.70% isopropyl alcohol prep; gray sodium fluoride/potassium oxalate tube

    An alcohol-based antiseptic can contaminate the specimen and, more importantly, gives the defense a basis to challenge the result, so a non-alcohol antiseptic such as aqueous benzalkonium chloride, povidone-iodine, or soap and water is used instead. The gray tube is required because sodium fluoride inhibits glycolysis and microbial fermentation, which would otherwise change the ethanol concentration in the tube before analysis. Chain-of-custody documentation must accompany the specimen.

    Source: CLSI PRE02-Ed8, site antisepsis for blood alcohol collection (non-alcohol antiseptic) with sodium fluoride/potassium oxalate tubeReport a problem with this question

20. 20. Two different evacuated tubes carry a yellow stopper. How do they differ?

    • A.Both contain SPS; the difference is only in manufacturer shading
    • B.Both are drawn last, after the gray tube
    • C.The SPS tube is for HLA typing and the ACD tube is for blood cultures
    • D.The SPS tube is for blood cultures and is drawn in the first, sterile position; the ACD tube is for HLA typing, paternity, and DNA studies and is not drawn first✓ Answer

    Color alone cannot place a yellow tube — the additive does. Sodium polyanethol sulfonate (SPS) is an anticoagulant that also inhibits complement, phagocytes, and certain antibiotics, so it supports microbial recovery and occupies the sterile first position with blood cultures. Acid citrate dextrose (ACD) preserves cell viability and DNA for HLA typing, paternity, and DNA studies, and is not a sterile-first specimen. Conflating the two is a common error precisely because the stopper color is shared.

    Source: CLSI PRE02-Ed8: sterile blood culture tubes (yellow SPS) first; ACD tubes placed by additive, not stopper colorReport a problem with this question

21. 21. Where does a royal blue trace-element/toxicology tube belong in the order of draw?

    • A.Immediately after the light blue citrate tube, regardless of additive
    • B.Always last, after the gray tube
    • C.It depends on its additive: the clot-activator version draws with the serum tubes and the EDTA version draws with the EDTA tubes✓ Answer
    • D.Always first, ahead of the blood culture bottles

    Royal blue is a certified low-trace-metal tube manufactured in more than one additive version — a clot-activator (serum) version and a Na2/K2EDTA (plasma) version — so it has no single fixed slot. Applying the general rule that an unfamiliar tube is placed by its ADDITIVE rather than its color puts the serum version in step 3 and the EDTA version in step 5. A facility may adopt a documented alternate order (for example, drawing trace-metal tubes first to avoid stopper contact) only with supporting validation data.

    Source: CLSI PRE02-Ed8: tubes not named among the six steps are positioned by their additive; royal blue is available with clot activator or with Na2/K2EDTAReport a problem with this question

22. 22. During equipment quality control, several evacuated tubes are found to be past their expiration date. Why must they not be used?

    • A.Expired tubes are acceptable as long as the additive still appears clear
    • B.Expiration affects only the label adhesive, so the tubes may be relabeled and used
    • C.Expired tubes may have lost vacuum and additive reactivity, causing short draws and an incorrect blood-to-additive ratio✓ Answer
    • D.Expired tubes are acceptable if they have been kept refrigerated

    The expiration date is the manufacturer's guarantee of both the preset vacuum and the additive's potency. Past that date the tube may draw less than its stated volume, which throws off the blood-to-additive ratio (critical for citrate and EDTA tubes), and a degraded additive may fail to anticoagulate or to preserve the analyte. Refrigeration and a clear-looking additive do not restore either property. The same pre-use inspection should reject cracked tubes, cloudy or discolored additive, bent or barbed needle points, and any device whose sterility seal is already broken; stock is rotated first-in, first-out.

    Source: CLSI PRE02-Ed8, collection device quality control: verify expiration dates and device integrity before useReport 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 →