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The determination of INR in stored whole blood
D R Leeming1, S Craig, K J Stevenson
1Thrombosis Reference Centre, Withington Hospital, Manchester, UK.
Insights
Storing whole blood samples for international normalised ratio (INR) testing is unreliable. Significant INR changes can occur within 24 hours, potentially affecting patient anticoagulant dosage.
Area of Science:
- Clinical Pathology
- Hematology
Background:
- Accurate monitoring of oral anticoagulant therapy is crucial for patient safety.
- International Normalised Ratio (INR) is a standard measure for monitoring warfarin therapy.
- The stability of whole blood samples during storage impacts INR determination accuracy.
Purpose of the Study:
- To assess the reliability of INR measurements from whole blood samples stored at room temperature for up to 48 hours.
- To evaluate the impact of storage duration on INR values across different prothrombin time systems.
Main Methods:
- INR was determined for 40 patients on fresh blood and samples stored for 24 and 48 hours.
- Five different prothrombin time systems were used for analysis.
- Coagulation factors II, V, VII, and X were measured in a subset of patients before and after incubation.
Main Results:
- INR values varied significantly between storage durations and testing systems.
- Individual INR changes exceeding 0.5 were observed within 24 hours for all systems, potentially altering patient dosage.
- After 48 hours, INR changes were more pronounced across most systems, except for Recombiplastin.
Conclusions:
- Whole blood sample storage for INR determination, even for 24 hours, can lead to clinically significant changes.
- The practice of storing whole blood samples for INR analysis is not recommended due to compromised reliability.
Aims:
To examine the reliability of international normalised ratio (INR) determination on samples stored as whole blood for up to two days at room temperature.
Methods:
The INR of 40 patients receiving oral anticoagulants was determined on fresh blood and on samples stored for 24 and 48 hours, using five locally calibrated prothrombin time systems. These incorporated Manchester reagent, Recombiplastin, IL PT Fibrinogen HS Plus, Manchester combined capillary prothrombin time reagent, and a freeze dried in-house reference rabbit brain thromboplastin, RBT 1010. In addition, factors II, V, VII, and X were determined on samples obtained from 18 of these patients before and after incubation at room temperature.
Results:
The INR of the samples changed by differing amounts during storage, depending on which system was employed. Although the mean change after 24 hours storage was relatively small, there were individual samples that changed by > 0.5 INR with all systems. These changes would lead to adjustment in dosage of certain patients. After 48 hours these effects were greater with all systems except that employing Recombiplastin. There were only small reduction in the measured factors by 48 hours.
Conclusions:
After storage of samples for only 24 hours, some patients' INR changed sufficiently to affect dosage. In view of these observations, the practice of storing whole blood samples for INR determination cannot be recommended.
