NHA Phlebotomy Technician (CPT) — All Questions

A phlebotomist must collect a blood culture set, a PT/INR, a basic metabolic panel on a gel serum tube, and a CBC. Which collection sequence follows the standard order of draw?

• a.Blood culture, light blue, gel serum tube, lavender✓
• b.Light blue, blood culture, lavender, gel serum tube
• c.Gel serum tube, blood culture, light blue, lavender
• d.Lavender, light blue, blood culture, gel serum tube

The standard order of draw is blood culture (sterile) first, then the light blue sodium citrate coagulation tube, then serum tubes with or without gel, then heparin, then EDTA, then glycolytic inhibitor tubes. Drawing the blood culture first protects it from skin-flora contamination introduced by non-sterile tube handling. Every other sequence listed allows additive carryover into a tube where that additive causes error, most notably EDTA carried into a chemistry or coagulation tube.CLSI GP41

A phlebotomist accidentally draws the lavender EDTA tube before the light blue citrate tube. What is the most likely consequence for the coagulation results?

• a.The specimen will clot in the light blue tube within seconds
• b.There is no effect because both tubes contain anticoagulants
• c.The PT and aPTT will be falsely shortened by the added EDTA
• d.EDTA carryover chelates calcium and can falsely prolong the PT and aPTT✓

EDTA is a potent calcium chelator, and even a trace carried over on the needle into the citrate tube removes additional calcium and can falsely prolong clotting times. It may also falsely raise potassium and lower calcium if carried into a chemistry tube. The tubes are not interchangeable simply because both are anticoagulated; each anticoagulant works by a different mechanism and only citrate is validated for routine coagulation testing.CLSI GP41

A patient has small veins and the phlebotomist leaves the tourniquet in place while palpating for two full minutes. What analytic problem is most likely?

• a.Dilution of the specimen with interstitial fluid
• b.Loss of platelets from the sample
• c.Hemoconcentration with falsely elevated protein, calcium and potassium✓
• d.Complete clotting of the EDTA specimen

The tourniquet should stay on no longer than one minute; beyond that, plasma water leaves the vessel and protein-bound and cellular analytes concentrate. This produces falsely elevated total protein, albumin, calcium, potassium and hematocrit. Tourniquet time does not dilute the sample or cause the EDTA tube to clot, and platelets are not selectively lost.CLSI GP41

Which antecubital vein is the first choice for routine venipuncture in an adult?

• a.Median cubital vein✓
• b.Basilic vein
• c.Radial vein
• d.Brachial vein

The median cubital vein is selected first because it is usually large, well anchored, close to the surface and farthest from the brachial artery and median nerve. The basilic vein is the last antecubital choice precisely because the artery and nerve lie beneath it. The brachial and radial vessels are deep or arterial and are not used for routine venipuncture.CLSI GP41

At what angle to the skin should the needle be inserted for a routine antecubital venipuncture?

• a.90 degrees
• b.15 to 30 degrees✓
• c.5 degrees or less
• d.45 to 60 degrees

A 15 to 30 degree angle allows the bevel to enter the vein lumen without passing through the far wall. An angle that is too shallow causes the needle to ride on top of the vein and fail to enter; an angle of 45 degrees or more risks going through the vein and into underlying structures. A 90 degree insertion is used for dermal puncture devices, not for venipuncture.CLSI GP41

Which needle gauge range is standard for routine adult venipuncture with an evacuated tube system?

• a.25 to 27 gauge
• b.16 to 18 gauge
• c.18 to 20 gauge
• d.21 to 23 gauge✓

Gauges 21 to 23 are standard: 21 is the general-purpose size, 22 is used for smaller or fragile veins, and 23 is typical of a winged (butterfly) set. Larger bores such as 16 to 18 gauge are used for blood donation or infusion and are unnecessarily traumatic for diagnostic draws. Very small bores like 25 gauge force cells through a narrow lumen and cause hemolysis.CLSI GP41

A provider orders a lactate and a blood alcohol level. Which tube additive combination is designed to preserve these analytes?

• a.K2 EDTA
• b.Lithium heparin
• c.Sodium citrate
• d.Sodium fluoride and potassium oxalate✓

The gray-top tube contains sodium fluoride, an antiglycolytic agent that stops cells from consuming glucose or generating lactate, plus potassium oxalate as the anticoagulant. Citrate is for coagulation testing, heparin for stat chemistry, and EDTA for hematology; none of them inhibit glycolysis. Note that a non-alcohol antiseptic must also be used when collecting a blood alcohol.CLSI GP41

The light blue stopper tube used for PT/INR and aPTT contains which additive, and why must it be filled completely?

• a.Sodium citrate, because a fixed 9:1 blood-to-anticoagulant ratio is required✓
• b.Thrombin, because clotting must be accelerated
• c.EDTA, because underfilling shrinks the red cells
• d.Heparin, because it must be balanced against the plasma volume

Sodium citrate reversibly binds calcium and requires a 9 parts blood to 1 part anticoagulant ratio. An underfilled tube leaves excess citrate that binds reagent calcium during testing and falsely prolongs the PT and aPTT. Heparin and EDTA are not used for routine coagulation, and thrombin is found in rapid-serum tubes, not coagulation tubes.CLSI GP41

A comprehensive metabolic panel is ordered. Which tube is appropriate and what does it contain?

• a.Gray tube containing sodium fluoride
• b.Light blue tube containing sodium citrate
• c.Gold or tiger-top serum separator tube containing a clot activator and gel✓
• d.Lavender tube containing K2 EDTA

Chemistry panels are run on serum from a serum separator tube, which holds a clot activator plus a thixotropic gel that forms a barrier between serum and cells after centrifugation. Citrate tubes are for coagulation, EDTA for hematology, and fluoride for glucose and alcohol preservation. Using an anticoagulated tube in place of the SST changes several chemistry values.CLSI GP41

A stat ammonia level is ordered. Which tube is used and where does it fall in the order of draw?

• a.Green heparin tube, drawn after serum tubes and before EDTA✓
• b.Lavender EDTA tube, drawn before the serum tube
• c.Light blue citrate tube, drawn first
• d.Gray fluoride tube, drawn before heparin

Ammonia is collected in a heparin tube, and heparin tubes are drawn after serum tubes and before EDTA in the standard order. The specimen must also be placed on ice and delivered promptly because ammonia rises quickly at room temperature. EDTA, citrate and fluoride tubes are not appropriate for ammonia and none of them occupy the heparin position in the sequence.CLSI GP41

Which group of tests is collected in the lavender EDTA tube?

• a.Comprehensive metabolic panel and lipid panel
• b.Glucose, lactate and blood alcohol
• c.CBC, hemoglobin A1c and ESR✓
• d.PT, aPTT and fibrinogen

EDTA preserves cell morphology and prevents platelet clumping, so it is the tube of choice for the CBC, hemoglobin A1c and the erythrocyte sedimentation rate. Coagulation tests require citrate, glucose and alcohol require a fluoride tube, and chemistry panels require serum or heparinized plasma. Substituting EDTA for a chemistry tube falsely raises potassium and falsely lowers calcium.CLSI GP41

What is the maximum lancet penetration depth for a heel stick on a newborn?

• a.2.0 mm✓
• b.5.0 mm
• c.3.5 mm
• d.There is no depth limit if the heel is warmed

Penetration must not exceed 2.0 mm because the calcaneus in a newborn may lie only 2 to 3 mm below the plantar skin, and bone contact can cause osteomyelitis. Depths of 3.5 mm or 5 mm greatly increase that risk. Warming the heel improves blood flow but does not change the safe depth limit.CLSI GP42

A phlebotomist is preparing a heel stick on a two-day-old infant. Which site is acceptable?

• a.The posterior curvature of the heel
• b.The medial or lateral plantar surface of the heel✓
• c.The great toe
• d.The arch of the foot

Only the medial and lateral plantar surfaces of the heel are used, because the calcaneus does not extend into these areas. The posterior curvature sits directly over the bone, and the arch overlies nerves, tendons and cartilage. The great toe and other fingers or toes are not acceptable dermal puncture sites in a newborn.CLSI GP42

During a capillary collection the phlebotomist must fill a lavender microtube and a serum microtube. Which order is correct?

• a.Both must be filled at the same time from separate punctures
• b.Either order, because capillary blood has no additive carryover
• c.Lavender microtube first, then serum✓
• d.Serum microtube first, then lavender

The capillary order of draw differs from venipuncture: after any blood gas specimen, EDTA is collected first so that platelets are captured before they aggregate at the puncture site, followed by other additive tubes and finally serum. Filling the serum tube first would leave a clumped, unrepresentative platelet count. Carryover and clotting both occur in capillary work, so order does matter and a second puncture is not required.CLSI GP42

A phlebotomist cleans the site with 70% isopropyl alcohol and inserts the needle immediately while the skin is still wet. What is the most likely result?

• a.The venipuncture will be less painful for the patient
• b.Stinging for the patient and hemolysis of the specimen✓
• c.The antiseptic effect will be improved
• d.The specimen will clot faster in the tube

Alcohol must air dry for about 30 seconds so it can kill organisms and so residual alcohol is not carried into the vein. Wet alcohol stings on needle entry and lyses red cells, producing hemolysis that falsely raises potassium, LDH and AST. Drying is part of the antiseptic action, so puncturing early reduces rather than improves disinfection.CLSI GP41

Which skin antisepsis is appropriate before collecting blood cultures from an adult?

• a.Soap and water only
• b.A single wipe of 70% isopropyl alcohol
• c.No antisepsis is needed because the bottles are sterile
• d.Chlorhexidine gluconate applied with friction and allowed to dry completely✓

Blood cultures require an antiseptic effective against resident skin flora, and chlorhexidine gluconate applied with friction and fully dried is the standard for patients older than two months. A quick alcohol wipe alone does not reduce skin flora enough and leads to false-positive contaminated cultures. Sterile bottles do not protect against organisms carried in on the needle from unprepared skin.CLSI GP41

An inpatient has an IV infusing in the left forearm and no accessible veins in the right arm. What is the best action?

• a.Cancel the order and document that no site was available
• b.Ask the nurse to stop the infusion, wait at least two minutes, then draw below the IV and discard the first 5 mL✓
• c.Draw from the IV line without flushing it
• d.Draw directly above the IV site with the infusion running

When no other site exists, the infusion is stopped by licensed personnel, a short wait allows the fluid to clear, the draw is made distal to the IV so blood has not passed the infusion point, and a discard volume clears residual fluid. Drawing above a running IV dilutes the specimen with infusate. Drawing from a line without flushing gives contaminated results, and simply canceling the order abandons a resolvable problem.CLSI GP41

A patient had a right mastectomy with lymph node removal 14 months ago and has an IV in the left hand. What should the phlebotomist do?

• a.Consult the patient's provider for guidance before selecting a site✓
• b.Draw above the IV in the left arm
• c.Draw from the right antecubital area since the surgery was over a year ago
• d.Use a fingerstick on the right hand without asking anyone

Lymph node dissection impairs lymph drainage indefinitely, so the affected side is avoided because of infection and lymphedema risk, and there is no automatic time limit that makes it safe. With the only other arm carrying an IV, the correct step is to obtain provider direction rather than choose unilaterally. Drawing above an IV dilutes the sample, and a fingerstick on the affected side carries the same restriction as a venipuncture.CLSI GP41

Why is the basilic vein the last antecubital choice for venipuncture?

• a.It is too small to accommodate a 21 gauge needle
• b.The brachial artery and median nerve lie close beneath it✓
• c.It collapses under vacuum more easily than other veins
• d.It contains more valves than any other arm vein

The basilic vein sits on the medial side of the antecubital fossa directly over the brachial artery and near the median nerve, so puncture there carries the highest risk of arterial nicking and nerve injury. Size, collapse tendency and valve count are not the deciding factors. When the basilic vein must be used, the needle is anchored carefully and the patient is monitored for shooting pain.CLSI GP41

A light blue tube is filled only two thirds of the way because the vein collapsed. What should the phlebotomist do?

• a.Add saline to the tube to reach the fill line
• b.Send it and note 'short draw' on the requisition
• c.Discard the tube and recollect a properly filled citrate tube✓
• d.Pour the contents into a second light blue tube to reach the fill line

A short-filled citrate tube violates the required 9:1 ratio and produces falsely prolonged PT and aPTT results, so it must be recollected rather than reported with a comment. Combining two partially filled tubes doubles the anticoagulant relative to blood and makes the error worse. Adding any diluent to an evacuated tube is never acceptable because it alters both the ratio and the analyte concentration.CLSI GP41

How should an EDTA tube be mixed immediately after collection?

• a.Invert once and place upright in the rack
• b.Invert gently 8 to 10 times✓
• c.Do not mix; the additive dissolves on its own
• d.Shake vigorously five times

EDTA tubes require roughly 8 to 10 gentle inversions so the anticoagulant coats all the blood and microclots do not form. Vigorous shaking introduces mechanical trauma and hemolysis, which invalidates many tests. A single inversion or no mixing at all leaves clotted or clumped specimens that the laboratory must reject.CLSI GP41

A phlebotomist collects an aerobic and anaerobic blood culture set, then a green heparin tube, then a light blue citrate tube. What is the main problem?

• a.Heparin and citrate tubes cannot be drawn during the same venipuncture
• b.The citrate tube was drawn after heparin, so heparin carryover can prolong clotting times✓
• c.Blood cultures should never be drawn first
• d.There is no problem; the sequence is correct

The citrate tube must immediately follow the blood cultures and precede all serum and heparin tubes. Because heparin inhibits thrombin, carryover into the citrate tube can falsely prolong the aPTT. Blood cultures are correctly drawn first, and both tubes may be collected in one venipuncture as long as the sequence is respected.CLSI GP41

A phlebotomist has just filled a light blue citrate tube. According to the standard order of draw, which tube is collected next?

• a.Gold serum separator tube✓
• b.Gray sodium fluoride tube
• c.Green heparin tube
• d.Lavender EDTA tube

After the citrate tube, serum tubes with or without a gel separator are collected, followed by heparin, then EDTA, then the fluoride tube. Placing EDTA or fluoride earlier risks carrying potassium-containing or oxalate additives into chemistry tubes. Heparin also follows, not precedes, the serum tube in the standard sequence.CLSI GP41

A patient is told to pump the fist repeatedly while the tourniquet is on. Which result is most affected?

• a.Sodium, which may be falsely decreased
• b.Hemoglobin, which may be falsely decreased
• c.Platelet count, which may be falsely elevated
• d.Potassium, which may be falsely elevated✓

Vigorous fist pumping causes muscle cells to release potassium into the local circulation, so the measured potassium can be falsely high. Patients may make a fist once to help the vein, but repeated pumping is discouraged. Hemoglobin, sodium and platelet counts are not meaningfully changed by this mechanism.CLSI GP41

A coagulation specimen is the only tube ordered and a winged blood collection set will be used. What should be done first?

• a.Fill the citrate tube directly, since the tubing volume is negligible
• b.Use a 25 gauge needle to slow the fill rate
• c.Remove the tourniquet before attaching the citrate tube
• d.Draw and discard a tube first to prime the tubing air space✓

The air in a winged set's tubing displaces blood from the first tube, so a discard tube is drawn first to prime the line and preserve the 9:1 fill ratio. Filling the citrate tube directly would underfill it and falsely prolong clotting times. The tourniquet stays on until blood flow is established, and a 25 gauge needle is too small and would cause hemolysis.CLSI GP41

The last tube is filling. In what order should the phlebotomist complete the venipuncture?

• a.Remove the last tube, release the tourniquet, then withdraw the needle and apply pressure✓
• b.Release the tourniquet, remove the needle, then remove the last tube
• c.Apply pressure to the site, then remove the needle and tourniquet together
• d.Remove the needle, release the tourniquet, then remove the last tube

The tube is removed from the holder first so no vacuum pulls on the vein, the tourniquet is released next to lower venous pressure, and only then is the needle withdrawn and pressure applied. Pulling the needle out with the tourniquet still tight forces blood into the tissue and causes a hematoma. Removing a tube after the needle is out is impossible, and pressure cannot be applied while the needle is still in the vein.CLSI GP41

A 4-year-old needs a CBC and a basic metabolic panel. Which approach best matches pediatric practice?

• a.Use an 18 gauge needle to finish quickly
• b.Draw from a foot vein without provider approval
• c.Use a 23 gauge winged set with small-volume tubes and secure, gentle immobilization✓
• d.Apply the tourniquet for three minutes to enlarge the vein

Children have small, mobile veins and a limited total blood volume, so a 23 gauge winged set with pediatric-volume tubes reduces trauma and blood loss. A large 18 gauge needle is unnecessarily traumatic, prolonged tourniquet time causes hemoconcentration, and lower-extremity draws require provider authorization. Comforting and safely holding the child also improves success on the first attempt.CLSI GP41

An 88-year-old patient has thin skin, fragile veins and takes warfarin. Which modification is most appropriate?

• a.Slap the arm firmly to raise the vein
• b.Apply the tourniquet as tightly as possible
• c.Use a 16 gauge needle so the draw finishes faster
• d.Anchor the vein without dragging the skin, use a 23 gauge winged set, and hold pressure longer after the draw✓

Older skin tears easily and anticoagulated patients bleed longer, so gentle anchoring, a smaller winged needle and extended pressure after needle removal are appropriate. Slapping the arm and overtightening the tourniquet bruise fragile tissue and can rupture the vein. A large bore needle increases trauma without any benefit for a routine draw.CLSI GP41

A requisition lists the patient name and tests but has no ordering provider and no collection priority. What should the phlebotomist do?

• a.Collect the specimens and write in a provider name from the chart
• b.Collect the specimens and let the laboratory sort it out
• c.Stop and have the incomplete requisition corrected before collecting✓
• d.Collect only the tests the phlebotomist recognizes

Laboratory testing must be performed on an authorized, complete order, so an incomplete requisition is clarified with the ordering source before any blood is drawn. Writing in information the phlebotomist did not receive from the provider falsifies the record. Collecting first and deferring the problem risks an unauthorized draw and a redraw for the patient.CLIA

How should the needle be positioned as it enters the skin during venipuncture?

• a.Bevel down and against the direction of blood flow
• b.Bevel up and in line with the vein, pointing toward the heart✓
• c.Bevel up but angled across the vein at 45 degrees
• d.Bevel sideways at 90 degrees to the vein

The bevel faces up and follows the long axis of the vein so the sharpest point enters first and the opening sits inside the lumen. Bevel-down entry can occlude the opening against the vein wall and stop flow. Crossing the vein at a steep or perpendicular angle increases the chance of going through the far wall and causing a hematoma.CLSI GP41

A phlebotomist has attempted venipuncture twice on the same patient without obtaining blood. What is the correct next step?

• a.Attempt a third and fourth time on the same arm
• b.Stop and ask another qualified phlebotomist to attempt the draw✓
• c.Probe laterally with the needle already in place until blood appears
• d.Send the patient home and cancel the tests

Standard practice limits a phlebotomist to two attempts before handing the patient to another qualified collector, which protects the patient from repeated trauma. Blind lateral probing risks nerve damage and arterial puncture and is never acceptable. Canceling ordered tests without escalation deprives the provider of needed results.CLSI GP41

Blood flow stops shortly after a good flash is seen. Which corrective action is appropriate?

• a.Move the needle rapidly side to side to find the vein
• b.Ask the patient to pump the fist continuously for one minute
• c.Pull the needle nearly out and reinsert it at a new angle
• d.Rotate the needle slightly or advance it a small amount, and confirm the tube is fully seated✓

Loss of flow is often caused by the bevel resting against a vein wall, a partially seated tube or a collapsed vein, so gentle rotation, slight advancement or reseating the tube usually restores flow. Withdrawing and reinserting or moving the needle laterally can lacerate the vein and injure nerves. Continuous fist pumping falsely elevates potassium and does not solve a positional problem.CLSI GP41

Which fingerstick technique is correct for an adult capillary glucose?

• a.Puncture the center of the fingertip parallel to the fingerprint lines
• b.Puncture the tip of the fifth finger
• c.Puncture the side of the fleshy pad of the third or fourth finger, across the fingerprint lines✓
• d.Puncture the thumb because it has the best blood supply

The side of the fleshy pad of the middle or ring finger is used, and the puncture crosses the fingerprint lines so the drop forms rather than running along a groove. The very center of the fingertip is the most nerve-dense and painful area. The fifth finger has little tissue over bone and the thumb has a pulse and thicker calluses, so both are avoided.CLSI GP42

A legal blood alcohol specimen is ordered. Which site preparation is required?

• a.A non-alcohol antiseptic such as povidone-iodine or soap and water✓
• b.No cleaning at all, to avoid contaminating the sample
• c.70% isopropyl alcohol allowed to dry for one minute
• d.Alcohol followed by chlorhexidine

Alcohol-based antiseptics can contaminate the specimen and cast doubt on a legally defensible result, so a non-alcohol antiseptic is used. Chlorhexidine preparations frequently contain alcohol, so combining them does not solve the problem. Skipping antisepsis entirely violates infection control and would itself invalidate the collection.CLSI GP41

An order requires a lavender EDTA tube and a gray fluoride tube only. Which sequence is correct and why?

• a.Gray first, because it is the smallest tube
• b.Gray first, because the fluoride preserves glucose better when drawn early
• c.Either order, because neither additive affects the other
• d.Lavender first, because EDTA precedes the glycolytic inhibitor tube in the order of draw✓

In the standard sequence the EDTA tube always precedes the sodium fluoride and potassium oxalate tube, which is drawn last. Potassium oxalate carried backward into an EDTA tube can distort cell morphology and hematology results. Tube size and how early the fluoride is drawn have no bearing on the required order.CLSI GP41

A lavender EDTA tube is drawn before the gold gel serum tube and a small amount of EDTA is carried over. Which pattern of chemistry results is most consistent with that carryover?

• a.Potassium and calcium both falsely elevated, because EDTA salts preserve cations in the sample
• b.Potassium falsely elevated and calcium falsely decreased by the chelating additive✓
• c.Sodium falsely elevated and chloride falsely decreased by the added salt load
• d.Glucose falsely decreased because EDTA allows the red cells to keep consuming it

The common EDTA salts are dipotassium and tripotassium EDTA, so carryover adds potassium directly to the specimen and the reported potassium runs high. EDTA works by chelating calcium, so the calcium available for measurement is bound and the reported calcium runs low. Magnesium and alkaline phosphatase are affected the same way. Nothing in EDTA adds sodium or chloride, and EDTA does not inhibit glycolysis, so a glucose shift is not the signature of this error.CLSI GP41

A light blue sodium citrate tube for a PT/INR is filled to only about two thirds of its stated draw volume and is sent to the laboratory anyway. What effect does the short fill have on the result?

• a.The prothrombin time is falsely shortened because less anticoagulant reaches the plasma sample
• b.The prothrombin time is unaffected as long as the tube was inverted the correct number of times
• c.The prothrombin time is falsely prolonged, so the reported INR is too high✓
• d.The specimen clots in the tube, so no prothrombin time can be reported at all

The tube is manufactured so that a full draw gives nine parts blood to one part citrate. A short draw leaves the same fixed volume of citrate in a smaller volume of plasma, so excess citrate is still binding calcium when the laboratory adds its calcium-containing reagent. Clotting is therefore delayed and the time is reported longer than the patient's true value, which can lead a prescriber to reduce a warfarin dose that did not need reducing. Mixing does not correct a ratio problem, and a short draw does not by itself clot the specimen.CLSI GP41

By what mechanism does the heparin in a green stopper tube keep the specimen from clotting?

• a.It chelates the calcium in the specimen so that the coagulation cascade cannot proceed
• b.It coats the tube wall so platelets cannot adhere and form a clot
• c.It precipitates fibrinogen out of the plasma before the fibrin mesh can form
• d.It accelerates antithrombin, which then inhibits thrombin and factor Xa✓

Heparin is the only common tube anticoagulant that works by potentiating a natural inhibitor rather than by removing calcium. It binds antithrombin and greatly speeds that inhibitor's neutralisation of thrombin and factor Xa, so fibrin never forms. Chelation of calcium is how EDTA, citrate and oxalate work. Heparin does not precipitate fibrinogen, and no tube additive prevents clotting merely by coating the glass.

A gray stopper tube contains sodium fluoride and potassium oxalate. What does each of those two chemicals do?

• a.Fluoride inhibits glycolysis and preserves glucose; oxalate is the anticoagulant✓
• b.Fluoride is the anticoagulant; oxalate stabilises the red cell membrane
• c.Both act as anticoagulants, and the pair is used only because it is cheaper to produce
• d.Fluoride sterilises the specimen; oxalate keeps the glucose from crossing into the cells

Sodium fluoride is a preservative, not an anticoagulant: it blocks the glycolytic pathway so the red and white cells stop consuming glucose, which is why this tube is used for glucose, lactate and blood alcohol. Potassium oxalate does the anticoagulating, by precipitating calcium. Naming either chemical for the other job is the usual error, and fluoride has no meaningful sterilising or membrane-stabilising role at the concentration used.

Blood culture bottles and the yellow stopper sterile tube contain SPS. Besides preventing clotting, what does SPS contribute to a culture?

• a.It supplies the nutrients and the growth factors that an organism needs in order to multiply
• b.It lyses the red cells so that any organisms trapped inside them are released
• c.It inhibits complement, phagocytes and some antibiotics, so organisms survive to grow✓
• d.It selectively kills normal skin flora and leaves true pathogens undisturbed

Sodium polyanethol sulfonate anticoagulates and, just as importantly, blunts the blood's own antibacterial defences and some aminoglycoside activity, so a small number of organisms can still multiply in the bottle. It is not a nutrient; the broth in the bottle provides that. It does not lyse red cells, and no additive can tell a contaminating skin organism from a true pathogen, which is why careful skin antisepsis and two separate sites still matter.CLSI M47

A provider orders a serum lithium level on a patient taking lithium carbonate. Which tube choice matters here, and why?

• a.Use the light green lithium heparin gel tube, because the gel keeps the drug off the cells
• b.Avoid the lithium heparin tube, because the additive itself contains lithium✓
• c.Avoid the plain red tube, because glass activates and destroys lithium in the specimen
• d.Use the gray fluoride tube, because lithium is consumed by cells the way glucose is

A lithium heparin tube would add the very analyte being measured, so the reported concentration could be far above what the patient actually has and a real dose could be cut on the strength of it. A plain serum tube, or a sodium heparin tube where plasma is acceptable, avoids the problem. Glass does not destroy lithium, and lithium is not consumed by glycolysis, so a fluoride preservative has nothing to preserve.

In the standard order of draw, why is the green heparin tube collected before the lavender EDTA tube rather than after it?

• a.Heparin tubes clot faster than EDTA tubes, so they must be filled while the flow is best
• b.EDTA is supplied as a liquid additive and heparin as a spray-dried one, and liquids draw last
• c.Heparin carried into an EDTA tube destroys the white cells needed for a differential
• d.EDTA carried into a heparin tube would distort several chemistry and electrolyte results✓

The order of draw is arranged so that any additive dragged forward on the needle does the least harm. EDTA carried into a heparinised chemistry specimen raises potassium and lowers calcium, magnesium and alkaline phosphatase, so EDTA is placed after heparin rather than before it. Heparin carryover into an EDTA tube is undesirable but does not destroy white cells, and both additives can be supplied spray-dried.CLSI GP41

A stat basic metabolic panel is ordered on an inpatient. Why might the laboratory prefer a lithium heparin plasma tube over a gel serum tube?

• a.Plasma can be centrifuged as soon as it is mixed, while serum must clot first✓
• b.Plasma contains fibrinogen, and fibrinogen is required for accurate electrolyte measurement
• c.Serum tubes cannot be used at all for potassium, sodium, chloride or bicarbonate testing
• d.Plasma is drawn earlier in the order of draw, so the specimen spends less time on the needle

A serum tube has to be left upright long enough for the clot to form, typically about 30 minutes, before it can be spun. An anticoagulated plasma tube skips that wait entirely, which is why heparin tubes are common for stat chemistry. Plasma does contain fibrinogen, but that is a consequence of anticoagulation rather than a requirement for electrolytes, and serum is perfectly acceptable for a metabolic panel when time allows.

A phlebotomist fills a red clot activator tube first and then the light blue citrate tube for a PT/INR. What is the risk created by that sequence?

• a.Silica carried into the citrate tube dilutes the plasma and lowers every clotting factor
• b.Red tube additive has no effect on coagulation results because the red tube has no additive
• c.Clot activator carried forward can begin clotting and falsely shorten the clotting times✓
• d.The citrate tube will not fill after a serum tube because the vacuum has been used up

A red tube with clot activator is not additive-free. Silica particles dragged into a citrate tube start the very reaction the coagulation test is timing, so the plasma can clot faster than the patient truly would and an anticoagulated patient can look better controlled than they are. That is why the citrate tube is drawn before any serum tube. Carryover is a contamination problem, not a dilution problem, and each tube carries its own vacuum.CLSI GP41

How does the thixotropic gel in a serum separator tube do its job once the tube is centrifuged?

• a.It chemically bonds to the fibrin clot and drags the whole clot down to the bottom of the tube
• b.Its density lies between the cells and the serum, so it moves between the two layers✓
• c.It absorbs the serum and releases it slowly when the stopper is removed for testing
• d.It is heated by the friction of the spin and hardens into a plug across the tube

The gel is manufactured with a specific gravity between that of packed cells and that of serum. Under centrifugal force it becomes fluid, migrates to the position where those two densities meet, and sets there as a physical barrier that stops the cells from continuing to exchange potassium and glucose with the serum. It does not bond to fibrin, does not absorb serum, and does not depend on frictional heating.

The laboratory rejects a gel serum tube submitted for a therapeutic drug level and asks for a plain red tube instead. What is the usual reason for that policy?

• a.Gel tubes hold too little serum for the volume a drug assay needs to run in duplicate
• b.The clot activator in a gel tube chemically converts many drugs into inactive forms
• c.Drug levels must always be drawn into glass, and every gel tube is made of plastic
• d.Some drugs are absorbed by the gel, so the measured concentration drifts downward✓

Certain drugs, phenytoin and some tricyclic antidepressants among them, partition into the separator gel over time, so a level measured hours later can read lower than the patient's true concentration and prompt a dose increase that is not needed. Laboratories that see this specify a plain tube, and each laboratory publishes its own list. Volume, clot activator chemistry and the glass-versus-plastic question are not what drives the policy.

A pink stopper tube is ordered for a type and screen. What does that tube contain, and what is special about how it is labelled?

• a.Spray-dried EDTA, and it needs the collector's identification and the date and time✓
• b.Sodium citrate, and it is the one tube a facility may label at the nursing station later
• c.Lithium heparin, and it may be labelled from the requisition before the patient is seen
• d.No additive at all, and the blood bank supplies a pre-printed label for the armband

The pink blood bank tube is an EDTA tube, and it is the identification rather than the additive that most often causes harm. Blood bank policy requires the tube to be labelled at the patient's side with the patient identifiers plus who drew it and when, so a mistransfused unit can be traced. Labelling away from the patient, or before the draw, is exactly the practice that produces a wrong-blood-in-tube event.

Why does a laboratory require a royal blue stopper tube for a zinc or a lead level rather than an ordinary tube?

• a.The dark stopper colour shields the specimen from light that would break down the metal
• b.Royal blue tubes are manufactured to contain very little background trace metal✓
• c.The additive in a royal blue tube concentrates trace metals so low levels can be detected
• d.Royal blue tubes hold twice the volume that a trace element assay needs to run

Ordinary stoppers and tube walls contain enough trace metal to move a result that is reported in micrograms per decilitre, so a contaminated tube can turn a normal zinc into an abnormal one. Royal blue tubes are made under controlled conditions to keep that background as low as possible, and they come with EDTA, heparin or no additive depending on the test. Colour has no light-shielding role here, no tube concentrates an analyte, and volume is not the issue.

An erythrocyte sedimentation rate is ordered on a black stopper tube. What is distinctive about how that tube must be filled?

• a.It must be filled last so no additive from an earlier tube reaches it
• b.It is filled to any convenient level because the laboratory dilutes the blood again anyway
• c.It has a fixed blood to citrate ratio of four to one and must be filled to the line✓
• d.It is filled halfway on purpose to leave the air space the sedimentation column requires

The black sedimentation tube uses sodium citrate at a four to one ratio rather than the nine to one ratio of the light blue coagulation tube, and the dilution is part of the measurement. An underfilled or overfilled tube changes that dilution and moves the reported rate, so the fill line is not optional. The laboratory does not dilute again, no air space is required, and this tube is not simply the last one drawn.

A yellow stopper tube containing ACD solution is ordered. Which use is it intended for?

• a.DNA studies, HLA typing and parentage testing, which need viable cells✓
• b.Aerobic and anaerobic blood cultures drawn straight into a tube rather than into bottles
• c.Coagulation testing when the light blue citrate tube is unavailable from the supply room
• d.Trace element and toxicology work that would be spoiled by an ordinary stopper

Acid citrate dextrose preserves red cell viability and nuclear material, which suits it to HLA phenotyping, DNA studies and parentage testing. The other yellow tube, the sterile one, contains SPS and is the one used for culture, so the stopper colour alone does not identify the tube. ACD is not interchangeable with the coagulation citrate tube, whose ratio and concentration are different, and trace element work needs the royal blue tube.