Key result
In patients stabilized on long-term warfarin, factor concentrations were unequally depressed, with factor II accounting for 91% of the explained variance in the British corrected ratio.
Why the study?
What are the relative concentrations of vitamin K-dependent clotting factors in patients receiving long-term warfarin therapy?
Observational (n=37)
What are the relative concentrations of vitamin K-dependent clotting factors in patients receiving long-term warfarin therapy?
Long-term warfarin therapy depresses vitamin K-dependent clotting factors unequally, with factor II accounting for the vast majority of variance in the British corrected ratio.
Challenges assumption of equal factor depression by warfarin; leaves open whether INR monitoring requires factor II-specific refinement.
Using standard one stage clotting assays the concentrations of factors II, VII, IX and X were determined in 37 patients stabilised on warfarin for between three months and 17 years. Contrary to popular belief, the concentrations were not equally depressed, with factor X the lowest, factor II at intermediate value, factors VII and IX the highest. Some 71% of the variance of the British corrected ratio (BCR) could be accounted for by measurement of the factors assayed. Analysis of this variance showed 91% of the explained variance attributable to factor II, 7% to factor VII, 1.6% to factor IX and 0.4% to factor X. With the sudden and recent withdrawal of human thromboplastin, investigation of the sensitivities of the animal thromboplastins to changes in vitamin K dependent factors in orally anticoagulated patients is needed to ensure that the potentially alarming falls in factors II and X in these patients are being adequately detected.
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Paul et al. (1987) conducted an observational in Patients receiving long term warfarin (n=37). Warfarin was evaluated on Concentrations of factors II, VII, IX and X and variance of the British corrected ratio (BCR). In patients stabilized on long-term warfarin, factor concentrations were unequally depressed, with factor II accounting for 91% of the explained variance in the British corrected ratio.
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