Phlebotomy · Processing · 6 min read
Centrifuging and Aliquoting
- Explain the required clotting times, centrifuge balancing principles, and operational safety rules for blood specimen processing.
- Describe the appropriate emergency response, aerosol precautions, personal protective equipment, and decontamination steps for tube breakage in a centrifuge.
- Demonstrate proper aliquoting technique, secondary container labeling, and specimen preservation methods within the phlebotomist's scope of practice.
Clotting Requirements Prior to Centrifugation
Centrifugation separates the liquid portion of blood from the cellular components using centrifugal force. In routine processing, tubes collected for serum testing must be allowed to clot completely before they are placed into the centrifuge. Allowing tubes for serum testing to clot fully before centrifugation helps reduce fibrin strands in the separated serum. If blood is spun before clotting is finished, latent clot formation continues within the liquid layer. Centrifuging incompletely clotted blood causes fibrin strands that can clog automated analyzer probes during laboratory testing.
The time required for blood to solidify fully depends on the tube type and the additives present inside it. Non-additive red-top glass tubes generally require about 60 minutes to clot at room temperature before centrifugation; follow the tube manufacturer's instructions and laboratory protocol. Serum separator tubes with clot activators typically require 30 minutes to fully clot before spinning. When rapid processing is needed, tubes containing thrombin additives can clot in approximately 5 minutes. Phlebotomists must monitor these clotting periods carefully to protect testing instrumentation and ensure smooth workflow.
An everyday example of this principle is making gelatin: chilling the mixture before it has completely set produces a broken, watery mess with stringy clumps rather than a clean, firm gel. Similarly, rushing a blood tube into the centrifuge before the biochemical clotting cascade completes leaves loose fibrin strands floating throughout the serum.
| Tube Type and Additive | Required Clotting Time Before Spinning |
|---|---|
| Non-additive red-top glass tube | 30 to 60 minutes |
| Serum separator tube with clot activator | Typically 30 minutes |
| Tube containing thrombin additive | Approximately 5 minutes |
Common mistakes
- Re-centrifuging a gel separator tube to extract additional serum or plasma, which can disrupt the gel barrier and release intracellular components like potassium into the specimen.
- Opening the centrifuge lid immediately after hearing a tube break, rather than waiting at least 30 minutes for biohazard aerosols to settle.
- Pouring serum or plasma directly from the primary tube into an aliquot container instead of using a disposable transfer pipette, generating dangerous aerosols and splashes.
- Filling aliquot tubes destined for the freezer completely to the rim without leaving adequate headspace for liquid expansion.
Key points
- Centrifugation uses centrifugal force to separate liquid serum or plasma from cellular components, requiring capped tubes and balanced rotors.
- Tubes for serum testing must clot completely before spinning (30 to 60 minutes for non-additive red-top glass, 30 minutes for SSTs with clot activators, and approximately 5 minutes for thrombin tubes) to prevent fibrin strands from clogging analyzer probes.
- Unbalanced centrifuges cause excessive vibration, equipment damage, and tube breakage; balances must be compatible tubes adjusted to equal weight placed opposite one another.
- Centrifuge speed is measured in rpm, while relative centrifugal force (RCF) expresses acceleration in multiples of gravity (×g); excessive speed can cause red blood cell lysis, and insufficient force or spin time can cause incomplete separation.
- If a tube breaks in the centrifuge, keep the lid closed for at least 30 minutes to allow aerosols to settle, wear heavy-duty utility gloves, retrieve glass using mechanical devices like forceps or tongs, and discard glass in a rigid, puncture-resistant sharps container.
- Do not re-centrifuge gel tubes unless permitted by the manufacturer's instructions and laboratory protocol; re-centrifugation can disrupt the gel barrier and contaminate serum or plasma with cellular components.
- Aliquots must be transferred with disposable pipettes, capped tightly, given headspace if frozen, protected with amber containers or foil if light-sensitive, and labeled with at least two unique patient identifiers, specimen type, collection date/time, and collector identification.
Practice this section
Explained Phlebotomy Processing questions, no account needed. Phlebotomy Processing practice test
The full lesson continues with 4 more sections with exam tips, audio in English and Spanish, 5 Check yourself questions and 20 flashcards.
- 1 month
$41.99$20.99 - 3 months
$122.99$61.49 - Lifetime
$251.99$125.99
One payment, no subscription.
See Phlebotomy plansAlready a member? Log in
Sample lesson: Serum, Plasma and Clotting Before Centrifugation25 practice questions on this exam
Each Phlebotomy practice test has 25 original questions with the answers explained. No account needed.
Open the Phlebotomy practice testsOriginal lesson written for Phlebotomy practice · updated October 31, 2026. Exam names are trademarks of their owners; tests.global is not affiliated with them.