SST Tube Centrifugation Timeline
SST tubes should be centrifuged after allowing 30-60 minutes for clot formation at room temperature, with the entire process from collection to centrifugation completed within 2 hours to prevent biomarker degradation. 1
Optimal Processing Protocol
Immediate Post-Collection Steps
- Invert the tube 5 times immediately after blood draw (unless using glass red-top tubes) to mix blood with clot activators 1
- Place tubes upright at room temperature for 30-60 minutes to allow complete clot formation before centrifugation 1
Critical Time Windows
- The 2-hour rule is paramount: Total time from blood collection to centrifugation must not exceed 2 hours to minimize degradation of analytes, particularly sensitive biomarkers 1, 2
- If immediate centrifugation after clotting is not possible, refrigerate tubes at 4°C for no longer than 2 hours 1
- Serum must be separated from cells within 2 hours of centrifugation to prevent continued analyte degradation from cellular contact 1, 2
Centrifugation Parameters
- Centrifuge at 1500-2000 × g for 10 minutes at 4°C using horizontal rotors 1, 3
- Alternative rapid protocols of 3000 × g for 5-7 minutes are acceptable for most routine chemistry analytes without compromising analytical quality 4, 5
Extended Storage Considerations
When Delays Are Unavoidable
- Maximum refrigeration time before centrifugation: 24 hours at 4°C in unavoidable circumstances, though this significantly increases risk of biomarker degradation 1, 2
- After centrifugation and serum separation: samples can remain at 4°C for up to 4 hours before testing, though immediate testing is preferred 2
- Avoid direct contact with ice during refrigeration to prevent cell lysis 1
Long-Term Storage
- For storage beyond 4 hours post-separation: freeze serum at -80°C immediately 2
- Never use -20°C for clinical specimens as this causes protein degradation and spectral changes 1, 2
Critical Pitfalls to Avoid
Temperature Management
- Room temperature storage accelerates degradation exponentially compared to refrigeration, particularly for labile analytes like Alzheimer's disease biomarkers 2
- The 30-60 minute clotting period must occur at room temperature, not refrigerated, to ensure proper clot formation 1
Contact Time with Cells
- The 2-hour rule applies to total contact time between serum and cellular components, not just pre-centrifugation time 1, 2
- Post-centrifugation delay causes continued biomarker decline, though slower than pre-centrifugation delay 2
Centrifugation Technique
- Use horizontal rotors and set deceleration to lowest setting to prevent resuspension of the cellular layer 3
- Avoid excessive centrifugation speed or prolonged duration as this causes hemolysis and falsely elevates intracellular components like potassium, LDH, and AST 3, 4