SST Tube Testing Timeline After Collection
An SST tube should ideally be tested within 2 hours of collection after proper clotting and centrifugation, though serum can remain stable in the tube for up to 24 hours when refrigerated at 4°C. 1
Optimal Processing Timeline
The complete workflow from collection to testing follows this critical timeline:
Clotting Phase (30-60 minutes)
- SST tubes require 30 minutes of clotting time at room temperature before centrifugation 1
- Blood must sit upright during this period to allow proper clot formation 1
- Insufficient clotting leads to fibrin formation that clogs analyzers, while prolonged clotting causes cell lysis and serum contamination 1, 2
Pre-Centrifugation Delay (≤2 hours preferred)
- The entire process from collection to centrifugation should be completed within 2 hours 1
- This 2-hour window includes the 30-minute clotting time 1
- If immediate processing isn't feasible, refrigerate at 4°C for no more than 24 hours 1
- Room temperature storage beyond 2 hours causes progressive biomarker degradation, particularly for sensitive analytes like Aβ peptides 1
Centrifugation
- Centrifuge for 10 minutes at 1500-2000 × g at 4°C 1
- This separates serum from the clot and cellular components 1
Post-Centrifugation Storage and Testing
- Serum should be separated from cells and tested within 2 hours of centrifugation 1
- Serum left in contact with cells for more than 2 hours shows progressive analyte degradation 1
- Post-centrifugation delay causes slower but still significant biomarker decline compared to pre-centrifugation delay 1
Extended Storage Considerations
When immediate testing is impossible:
- Refrigeration at 4°C extends stability but should not exceed 24 hours before centrifugation 1
- After centrifugation and serum separation, samples can be stored at 4°C for up to 4 hours before testing 1
- For longer storage, freeze serum at -80°C immediately after separation 1
- Never store serum at -20°C for clinical purposes 1
Critical Pitfalls to Avoid
Temperature management is crucial: Room temperature storage accelerates degradation exponentially compared to refrigeration 1. The impact is particularly severe for labile analytes.
Contact time with cells matters: The 2-hour rule applies to total contact time between serum and cellular components 1. Once centrifuged, transfer serum to a secondary tube promptly.
Specific analyte considerations: While most routine chemistry tests remain stable for 24-72 hours in SST tubes 3, 4, specialized biomarkers (particularly Alzheimer's disease markers) are far more sensitive to delays 1.