Specimen Handling and Processing
Specimen Handling and Processing
The Specimen Handling and Processing domain covers the preanalytical steps that occur after collection: transport, centrifugation, separation, aliquoting, storage, and rejection. The exam tests whether you can preserve specimen integrity and recognize conditions that invalidate results.
Core rules
- Transport specimens promptly. Most serum and plasma tubes travel at room temperature; blood gas syringes, ammonia, and lactate specimens go on ice, while light-sensitive analytes are wrapped in foil.
- Allow serum tubes to clot for 30 minutes at room temperature before centrifugation; do not centrifuge immediately.
- Centrifuge at the manufacturer's specified speed and time, commonly 1,000-1,300 g for 10-15 minutes. Use a balanced load and follow any brake-off requirement.
- Separate serum or plasma from cells within 2 hours of collection. Leaving blood on cells causes glucose to fall and potassium to rise.
- Aliquot into labeled tubes that include the patient's full name, identifier, date, time, and specimen type.
- Store according to stability: refrigerate most routine chemistry and hematology specimens; freeze plasma only for tests that require it; never freeze whole blood for routine testing.
- Reject specimens that are unlabeled, mislabeled, grossly hemolyzed, clotted in an EDTA tube, in the wrong tube, or below the minimum fill volume.
Worked example
A serum tube for glucose and potassium arrives in the laboratory 3 hours after collection and has not been centrifuged. The glucose is 82 mg/dL and potassium is 6.1 mmol/L, while the patient's earlier results were glucose 110 mg/dL and potassium 4.2 mmol/L. The delay allowed glycolysis to lower glucose and red cell leakage to raise potassium. The specimen should be rejected and recollected, and the laboratory should document the preanalytical error. If the same tube had been centrifuged and separated within 30 minutes, both results would better reflect the patient's condition.
Traps
- Refrigerating whole blood before separation: cold storage can increase potassium release and hemolysis.
- Thawing frozen plasma in a microwave or hot water: protein denaturation and factor loss.
- Centrifuging a tube with a cracked cap: aerosol exposure and sample loss.
- Ignoring lipemia: marked lipemia interferes with many photometric assays and may require ultracentrifugation or a fasting recollect.
- Using a serum tube for a stat ammonia: ammonia requires prompt ice transport and plasma separation.