Phlebotomy Practice Test

Phlebotomy Processing Practice Questions

Processing makes up 7 of every 50 questions on a Tigertest Phlebotomy practice test. Here are 10 of the 28 questions on it, each with the answer and the reason.

Updated 2026-11-10 by the Tigertest team. Weighted to the NHA CPT test plan. Order of draw and technique follow CLSI GP41 and GP42.

1. 1. A processor has five patient tubes to centrifuge together in a six-place rotor. What must be done before starting the run?

   • A.Remove the stoppers so pressure can escape during the spin
   • B.Add an equal-volume balance tube opposite the odd tube
   • C.Lower the speed so the uneven load does not matter at all
   • D.Group all five tubes together on one side of the rotor

   Answer: B. Tubes must sit opposite tubes of equal volume and weight, so an odd tube is balanced with a water-filled tube of the same size and fill. Lowering the speed does not correct an unbalanced load, which vibrates and can break tubes.

2. 2. To save time, a new processor wants to remove tube stoppers before centrifuging serum specimens. Why must stoppers stay on during centrifugation?

   • A.To keep the gel barrier from melting
   • B.To help the clot form faster in the rotor
   • C.To stop red cells from settling too quickly
   • D.To prevent aerosols and evaporation

   Answer: D. Spinning an open tube releases infectious aerosols and lets the specimen evaporate, concentrating analytes; the centrifuge lid must also stay closed. Stoppers play no role in clotting, which must be complete before the spin.

3. 3. A gold-top SST for a comprehensive metabolic panel was collected two minutes ago from a patient not on anticoagulants. How long should it stand before centrifuging?

   • A.30 to 60 minutes, upright
   • B.No wait, because gel tubes can be spun at once
   • C.5 minutes, lying flat on its side
   • D.At least 4 hours in the refrigerator

   Answer: A. Serum tubes must clot completely, about 30 to 60 minutes upright at room temperature, before spinning. Gel does not remove the need to clot, and spinning too early leaves fibrin strands that can clog analyzers.

4. 4. After centrifugation, a technologist asks the processor to spin an SST a second time to get more serum. Why should gel separator tubes not be re-centrifuged?

   • A.The serum begins clotting a second time
   • B.The gel dissolves permanently into the serum
   • C.Cell contents can leak into the serum
   • D.The tube label smears inside the rotor

   Answer: C. A second spin can disturb the gel barrier and let potassium and other cell contents pass into the serum, and may hemolyze cells, giving false results. Re-spinning does not dissolve the gel; it compromises the separation.

5. 5. A laboratory procedure lists centrifuge settings as relative centrifugal force (RCF) rather than rpm. Why is RCF the better setting to specify?

   • A.It is identical to rpm on every centrifuge model
   • B.It sets the length of each run automatically
   • C.It accounts for rotor radius as well as speed
   • D.It measures the specimen temperature during the spin

   Answer: C. RCF is the actual force on the specimen and depends on both rpm and the rotor radius, so the same rpm gives different forces on different centrifuges. That is why rpm alone cannot be transferred between instruments.

6. 6. A processor divides serum from one SST into three aliquot tubes for chemistry, immunology and a reference lab. How should the aliquot tubes be labeled?

   • A.Each with the original tube's patient identifiers
   • B.With the patient's room number and the test name
   • C.After testing, once the results have been verified
   • D.Only the original tube needs full patient labeling

   Answer: A. Every aliquot is a separate specimen and must carry the same identifiers as the primary tube, plus the specimen type when required. A room number is never an identifier, and an unlabeled aliquot is rejected.

7. 7. A phlebotomist is explaining to a student how serum and plasma differ. Which statement is correct?

   • A.Serum contains fibrinogen; plasma does not
   • B.Serum comes from tubes containing an anticoagulant
   • C.Plasma is obtained only after the blood clots
   • D.Plasma contains fibrinogen; serum does not

   Answer: D. Plasma comes from anticoagulated blood and keeps its clotting factors, including fibrinogen. Serum is the liquid left after clotting, so its fibrinogen has been used up forming the clot.

8. 8. A plasma catecholamine specimen must be chilled immediately after collection for transport to the laboratory. Which method is correct?

   • A.Keep the tube in a 37 C heat block
   • B.Immerse the tube in an ice-water slurry
   • C.Lay the tube directly on solid ice cubes
   • D.Place the whole blood tube in the freezer

   Answer: B. An ice-water slurry cools the whole specimen evenly. Solid ice cubes cool unevenly and can freeze parts of the tube, causing hemolysis, and freezing whole blood ruptures red cells.

9. 9. A cryoglobulin specimen has been collected and must stay at body temperature until the serum is separated. Which transport method is correct?

   • A.An ice-water slurry in a transport cup
   • B.A 37 C heat block or warm carrier
   • C.A refrigerator set at 2 to 8 C
   • D.An amber bag kept at room temperature

   Answer: B. Cryoglobulins precipitate when cooled below body temperature, so the specimen is kept at 37 C until separated. Chilling it, as is done for ammonia, would make the protein drop out and give a falsely low result.

10. 10. A phlebotomist collects an ammonia on ice and a separate tube for potassium. How should the potassium tube be handled before centrifugation?

    • A.Frozen as whole blood until it is spun
    • B.Chilled in the slurry along with the ammonia
    • C.Kept warm in a 37 C heat block
    • D.Kept at room temperature, not iced

    Answer: D. Chilling whole blood slows the cells' sodium-potassium pump, so potassium leaks out and is falsely elevated. Only analytes such as ammonia need ice; potassium stays at room temperature and is separated promptly.