Preserving blood samples for accurate PT and APTT results requires precise steps to prevent coagulation errors and maintain sample integrity. Key steps include proper collection in 3.2% sodium citrate tubes, mixing, centrifugation, and appropriate storage or transport.
Proper preservation of blood samples is essential to ensure accurate Prothrombin Time (PT) and Activated Partial Thromboplastin Time (APTT) results in the laboratory. Following the correct procedures prevents coagulation errors, maintains sample integrity, and ensures reliable testing outcomes.
To preserve blood samples effectively for PT and APTT testing, follow these steps:
- Sample Collection
- Mixing
- Centrifugation
- Storage Conditions
- Transport Considerations
- Quality Control
1. Sample Collection
- Use a 3.2% Sodium Citrate Tube: Collect the blood sample in a blue-top tube with a ratio of 1 part anticoagulant to 9 parts blood.
- Ensure Clean Venipuncture: This prevents hemolysis or activation of the coagulation cascade, which can compromise test results.
- Fill to the Correct Level: Maintain the precise anticoagulant-to-blood ratio to avoid errors in testing.
2. Mixing
- Invert the Tube Immediately: Gently invert the tube 3–4 times after collection to mix the anticoagulant with the blood and prevent clot formation.
3. Centrifugation
If testing cannot be performed immediately:
- Centrifuge at the Correct Speed and Time: Use 1500–2000 g for 10–15 minutes to separate plasma.
- Avoid Over-Centrifugation: Prolonged or high-speed centrifugation may affect the accuracy of results.
4. Storage Conditions
- Room Temperature (18–24°C):
- Perform PT testing within 24 hours of sample collection.
- Conduct APTT testing within 4 hours if the sample is not centrifuged or frozen.
- Frozen Plasma:
- Aliquot platelet-poor plasma into plastic tubes and freeze at -20°C or lower if immediate testing is not possible.
- For extended storage, use -70°C to preserve plasma for longer periods.
- Avoid repeated freeze-thaw cycles, which degrade clotting factors.
5. Transport Considerations
- Maintain Room Temperature During Transport: Avoid exposing the sample to extreme temperatures, such as excessive heat or cold.
- For Long-Distance Transport: Ship plasma aliquots on dry ice to maintain freezing conditions.
6. Quality Control
- Check for Sample Integrity: Ensure samples are free from hemolysis, lipemia, or clotting, as these can interfere with test results.
- Accurate Labeling: Label samples with all necessary details, including collection time, to prioritize timely analysis.
Conclusion
By adhering to these guidelines, you can ensure reliable and reproducible PT and APTT results. Proper sample collection, handling, and storage are critical for maintaining the integrity of coagulation studies and preventing errors.