3 Specimen Processing and Centrifugation

Preserve identity and condition

Correct processing helps preserve a specimen’s identity and condition from collection through testing. Delays, the wrong tube, temperature changes, and poor separation can alter results, so follow the laboratory’s current, test-specific instructions rather than assuming one centrifugation or storage setting works for every specimen.

Treat blood and other potentially infectious materials as biohazards. Use Standard precautions, appropriate personal protective equipment, leak-resistant containers, and approved spill and waste procedures. During transport, secure the primary container in suitable secondary containment to help contain leaks.

Identify the patient using the facility’s required identifiers, and label the specimen container at collection. Check that the label matches the requisition and that the specimen type, tube, collection time, and requested tests meet laboratory requirements. An unlabeled or mismatched specimen may no longer be reliably linked to the patient and may need to be rejected.

Prepare and transport specimens

Before processing, verify the specimen type, container, volume, and handling instructions. For blood tubes, confirm that the tube is adequately filled when the additive-to-blood ratio matters. Gently invert additive-containing tubes as directed by the manufacturer or laboratory; do not shake them. Serum tubes generally need time to clot before centrifugation. Anticoagulated plasma tubes should be mixed and handled according to their test instructions.

Transport specimens promptly, using the specified temperature and packaging conditions. Some specimens must remain at room temperature, others must be refrigerated, and certain tests require freezing or other special handling. Conditions and stability limits vary by test, so consult the current test directory instead of assuming one storage rule applies to all specimens.

Recognize specimen acceptance problems

A laboratory may reject a specimen for missing or conflicting identification, the wrong specimen or container, insufficient quantity, leakage, improper transport or temperature, or a specimen outside its stability limit. A clot in a tube that should contain anticoagulated blood is another possible reason for rejection. Hemolysis, clotting, or other quality problems may make a specimen unsuitable for particular tests.

Rejection rules depend on the test and laboratory. Document and report a problem; do not relabel or alter a specimen without authorization. If a specimen is unsuitable, follow the laboratory’s reporting and rejection procedures.

Set up and operate the centrifuge

Confirm whether the specimen should be centrifuged and check the required rotor or tube type, clotting time if applicable, Relative centrifugal force (RCF), duration, and temperature. The correct conditions depend on the test and collection system; a setting published for one laboratory or tube is not a universal setting.

Inspect the equipment and tubes before use. Use compatible tubes, buckets, and rotor components, and do not use cracked or damaged tubes. Keep the bowl and tubes dry, ensure the rotor is properly seated, and use safety cups or sealed rotors when required by the risk assessment and equipment instructions.

Balance the load by placing tubes of equal mass opposite one another. With an even number of positions, load symmetrically. Use a suitable balance tube containing compatible material when needed, and balance buckets and adapters as specified by the centrifuge manufacturer. Do not run a visibly unbalanced rotor.

Set the specified RCF and time, and set the temperature when required. Prefer RCF over Revolutions per minute (RPM): the same RPM can produce different forces in rotors with different radii. If conversion is needed, use the manufacturer’s calculator or this relationship:

Here, $r$ is the rotational radius in centimeters. Never exceed the maximum speed of the rotor or any other equipment component.

Close the lid and keep it closed during operation. If the centrifuge vibrates, makes an unusual noise, or otherwise behaves abnormally, stop it according to the operating procedure. Investigate only after the rotor has come to a complete stop; do not open the lid while it is moving.

Understand separation and blood components

Centrifugation separates components by spinning them at a specified force for a specified time. In a typical blood specimen, denser red blood cells move outward and settle below the less-dense liquid. Serum is obtained after blood has clotted; Plasma is obtained from blood collected with an anticoagulant and retains clotting factors.

The correct tube, clotting or mixing procedure, RCF, time, and temperature depend on the test and collection system. Use the specified conditions rather than applying a setting from another laboratory or tube as a universal rule.

Handle separated specimens

Wait until the rotor has stopped completely before opening the centrifuge. Remove tubes carefully and inspect the separation. In serum tubes, check that clotting and separation are adequate; in plasma tubes, check that cells are separated as required. Avoid disturbing the cell layer or gel barrier.

If serum or plasma must be transferred, use an appropriate pipette and a clean, correctly labeled transfer container. Avoid carrying cells or the Buffy coat into the aliquot. Keep the original specimen identified and maintain traceability to the patient and test request.

Store specimens and escalate problems

Store and transport separated specimens at the temperature and for the period specified for the test. If a tube breaks or a spill occurs, follow the laboratory’s reporting and cleanup procedures. When instructions are unclear, do not improvise a centrifuge setting or storage condition; contact the responsible laboratory.

• Specimen processing