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Phlebotomy specimen processing and centrifugation practice questions, with every answer explained

Processing is 14 of the 100 scored items on the NHA CPT exam. Answer 10 exam style questions on specimen processing and centrifugation and see exactly which concepts would cost you points on test day.

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Where the NHA CPT points are100 scored items
Routine Blood Collections
28
Safety and Compliance
26
Patient Preparation
20
Processing
14
Special Collections
12
Source: NHA CPT test plan (2025)You are here ↑
Score 0/0
Q1Separation time

Within what time frame should serum or plasma generally be separated from cells after collection?

What these specimen processing and centrifugation questions test

These questions cover separation time, centrifuge, stopper removal, aliquoting and serum gel tubes. Each one shows the correct answer and why every other option is wrong, so a miss tells you exactly what to review before the NHA CPT.

Separation timeCentrifugeStopper removalAliquotingSerum gel tubesData entryProcessingCentrifugationSerum and plasmaWrong tube

All 10 questions with answers explained

Prefer to read first? Every question from the practice set above, with the correct answer and why each wrong option is wrong.

Q1Within what time frame should serum or plasma generally be separated from cells after collection?
  1. Within 2 hours
  2. Within 24 hours
  3. Any time before testing
  4. Within 5 days

Answer: A. General guidance is to separate serum or plasma from cells within 2 hours of collection, unless the test's stability data allow otherwise, to prevent changes such as falling glucose and rising potassium.

Why not B: 24 hours allows significant changes in many analytes.

Why not C: Delays cause cell metabolism to alter results.

Why not D: Five days is far too long for unseparated blood.

Exam tactic: Spin and separate within 2 hours.

Q2When is it safe to open the centrifuge lid?
  1. Whenever the lid is unlocked
  2. While it is slowing down
  3. As soon as the run timer beeps at the end of the cycle
  4. After the rotor has completely stopped

Answer: D. The lid is opened only after the rotor has come to a complete stop. Opening early risks injury and aerosol exposure, and stopping the rotor by hand is never done.

Why not A: Always confirm the rotor has stopped, even if unlocked.

Why not B: A moving rotor can injure and spread aerosols.

Why not C: The rotor may still be spinning when the timer ends.

Exam tactic: Lid opens only at a full stop.

Q3What is the safest way to remove a tube stopper?
  1. Twist it off behind a splash shield
  2. Snap it off quickly while holding the tube over the sink
  3. Pop it off quickly with the thumb
  4. Pull it off using your teeth

Answer: A. Stoppers are removed with a gentle twisting motion behind a splash shield, often covered with gauze, to prevent aerosols and splashes. Popping the stopper sprays the specimen.

Why not B: Quick removal causes splashing and aerosols, sink or no sink.

Why not C: Popping creates aerosols and splashes.

Why not D: Never use the mouth for lab work.

Exam tactic: Twist, shield, gauze. Never pop.

Q4When pipetting plasma off a spun tube, what should be avoided?
  1. Using a new clean transfer pipette for each patient specimen
  2. Disturbing the cell layer and the buffy coat
  3. Labeling the aliquot
  4. Wearing gloves

Answer: B. The pipette tip stays above the cell layer so cells do not contaminate the plasma.

Why not A: A clean pipette is correct practice.

Why not C: Labeling is required.

Why not D: Gloves are required.

Exam tactic: Stay above the cells.

Q5A serum separator tube was already centrifuged. Why should it not be spun a second time?
  1. It will make the tube explode
  2. The gel barrier may be disrupted and alter results
  3. It will destroy the label barcode
  4. It will convert the separated serum into plasma below the gel

Answer: B. Recentrifuging a gel tube can disrupt the barrier and release cell contents such as potassium into the serum, giving false results.

Why not A: Tubes do not explode from a second spin; the concern is result accuracy.

Why not C: The barcode is not affected.

Why not D: Serum does not become plasma by being spun again.

Exam tactic: Gel tubes: spin once.

Q6Why must the collection time on the label be accurate?
  1. Results depend on timing and stability
  2. It decides which tube color the lab will use
  3. It is only for payroll
  4. It is not needed if the date is right

Answer: A. Accurate collection times are needed for timed tests, drug levels, stability limits and result interpretation.

Why not B: Tube color is chosen by the test, not the collection time.

Why not C: Collection time is a clinical requirement.

Why not D: Time matters as much as date for many tests.

Exam tactic: Real time on every label.

Q7A plasma test is ordered. Which tube can be centrifuged immediately after collection, without waiting for a clot to form?
  1. An anticoagulated tube
  2. A tube left uncapped overnight
  3. Any tube frozen before spinning
  4. A plain red tube after 60 minutes

Answer: A. Plasma comes from anticoagulated blood, so it can be centrifuged right away without waiting for clotting. Serum tubes must clot first.

Why not B: Leaving tubes uncapped overnight ruins specimens.

Why not C: Whole blood should not be frozen before separation.

Why not D: A plain red tube yields serum after clotting.

Exam tactic: Plasma: spin now. Serum: clot first.

Q8How must tubes be loaded into a centrifuge?
  1. All on one side, so the tubes can be removed faster when the run ends
  2. Balanced, equal tubes placed opposite each other
  3. With the stoppers removed
  4. In any position, the centrifuge balances itself

Answer: B. Opposite tubes must match in size and fill. A balance tube filled with water is used when needed.

Why not A: Loading one side unbalances the rotor and can damage the centrifuge or break tubes.

Why not C: Tubes stay capped to prevent aerosols.

Why not D: Centrifuges do not balance themselves.

Exam tactic: Balance it, opposite and equal.

Q9Which component is present in plasma but absent from serum?
  1. Fibrinogen
  2. Water
  3. Glucose
  4. Electrolytes

Answer: A. Plasma comes from anticoagulated blood and still has fibrinogen. Serum comes from clotted blood, and the fibrinogen is used up in the clot.

Why not B: Both contain water.

Why not C: Both contain glucose.

Why not D: Both contain electrolytes.

Exam tactic: Serum = plasma minus fibrinogen.

Q10A potassium level is received in a lavender K2EDTA tube. Why is it rejected?
  1. Lavender tubes have too little blood
  2. EDTA turns serum green
  3. The potassium in the EDTA additive contaminates the result
  4. Lavender tubes cannot be centrifuged, so no plasma is available for chemistry

Answer: C. K2EDTA contains potassium, which falsely raises the potassium result. Potassium is collected in a serum or heparin tube.

Why not A: Fill volume is not the reason.

Why not B: EDTA does not change serum color.

Why not D: EDTA tubes can be centrifuged when plasma is needed.

Exam tactic: K2EDTA means fake high K.

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More about the NHA CPT

PassPulse is an independent exam preparation tool. We are not affiliated with, endorsed by, or sponsored by the National Healthcareer Association (NHA), the American Society for Clinical Pathology (ASCP), the National Center for Competency Testing (NCCT) or American Medical Technologists (AMT). Exam, credential and product names mentioned on this page are trademarks of their respective owners and are used only to identify the exams described.

These practice questions are written by PassPulse to reflect the published exam content outline. They are not actual exam questions. Questions, answers and explanations may contain errors or be out of date, and they are for exam study only, not for clinical or professional practice: always check facts against the certifying body's official materials, current standards and your employer's policies. Scores and projections on this page are estimates based on a small number of questions and do not predict your result on the real exam. Area weights come from the official outline as of the date shown; always confirm current exam details with the certifying body.
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