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.
Answers are grounded in this paper and cite their sources.
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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