From the Guidelines
No, prothrombin time (PT) should not be performed using heparinized blood. This is because heparin can contaminate the sample and artificially prolong the PT result, leading to inaccurate measurements 1.
Key Considerations
- Heparin directly inhibits thrombin and other clotting factors, which are crucial for the extrinsic pathway that PT measures.
- The use of heparinized blood for PT testing can lead to unreliable results due to the enhancement of antithrombin activity, which inhibits several coagulation factors.
- To ensure accurate PT measurements, blood should be collected in sodium citrate tubes (light blue top) rather than heparin tubes (green top), with a proper blood-to-anticoagulant ratio (9:1) 1.
Best Practices for PT Testing
- Fill the sodium citrate tube completely to avoid underfilling, which can affect results.
- Avoid collecting the citrate tube first to prevent tissue factor contamination.
- Process the sample within 4 hours of collection to maintain accuracy, as prolonged storage can affect clotting factor activity.
Clinical Implications
- Inaccurate PT results can have significant clinical implications, including mismanagement of anticoagulation therapy and increased risk of thrombotic or bleeding complications.
- Therefore, it is essential to follow proper protocols for PT testing, including the use of sodium citrate tubes and careful handling of blood samples 1.
From the FDA Drug Label
- 1 Oral Anticoagulants Heparin sodium may prolong the one-stage prothrombin time. Therefore, when heparin sodium is given with dicumarol or warfarin sodium, a period of at least 5 hours after the last intravenous dose or 24 hours after the last subcutaneous dose should elapse before blood is drawn, if a valid prothrombin time is to be obtained.
The prothrombin time (PT) test cannot be reliably performed in heparinized blood, as heparin sodium may prolong the one-stage prothrombin time. To obtain a valid prothrombin time, a certain period should elapse after the last heparin dose before blood is drawn 2.
From the Research
Prothrombin Time in Heparinized Blood
- Prothrombin time (PT) is a coagulation assay that is typically performed on citrated plasma, not heparinized blood 3.
- Heparin can interfere with coagulation tests, including PT, and may cause prolonged results 4, 5.
- There are methods to remove heparin from plasma, such as using heparinase, which can improve the accuracy of PT results in patients treated with heparin 5.
- However, it is not recommended to perform PT on heparinized blood without proper treatment to remove the heparin, as this can lead to inaccurate results.
- The use of heparinized blood for PT testing is not a standard practice, and citrated plasma is the preferred sample type for this assay 6, 3.
- If heparinized blood is used, it may be necessary to use alternative methods, such as mixing studies, to interpret the results 7.