Key result
Warfarin therapy was associated with significant diurnal variations in prothrombin time and INR (p≤0.03), with a mean peak-to-trough difference of 1.8 ± 0.9 seconds.
Why the study?
Does long-term warfarin therapy cause diurnal variation in prothrombin time and INR over 24 hours compared to controls?
Observational (n=12)
No
Does long-term warfarin therapy cause diurnal variation in prothrombin time and INR over 24 hours compared to controls?
Prothrombin time and INR exhibit significant diurnal variation in patients on long-term warfarin therapy, peaking in the morning and reaching a trough in the evening, which may have clinical implications for monitoring.
Answers are grounded in this paper and cite their sources.
May warrant consistent INR sampling times in warfarin patients; leaves open effects on dosing or outcomes.
Study Objective . To determine the variation of prothrombin times and international normalized ratio (INR) over 24 hours in humans. Design . Prospective, parallel study. Setting . University‐affiliated general clinical research center. Patients . Six patients receiving long‐term warfarin therapy and six sex‐matched controls. Interventions . Warfarin was administered to the patients at 6:00 P.M. Measurements and Main Results . Prothrombin times and INR were determined every 2 hours over 24 hours. Time of study entry, meals, and sleep cycles were controlled. A significant cosinor rhythm for prothrombin times and INR (p≤0.03) occurred in warfarin‐treated patients, suggesting that diurnal variation occurs. The mean difference between the peak and trough prothrombin times was 1.8 ± 0.9 seconds (range 0.8‐3 sec) with a mean change of 9.3% ± 3.7%. The peak prothrombin time and INR values occurred between 4:00 A.M. and 8:00 A.M. in five patients, and trough values between 6:00 P.M. and midnight in five. No significant cosinor rhythm was noted for controls (p>0.5). Conclusion . Significant variations in prothrombin time and INR occurred in patients receiving warfarin therapy, with the highest values occurring in the morning and the lowest in the evening. These results may have clinical implications for patients receiving either high‐ or low‐intensity warfarin therapy.
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Bleske et al. (1995) conducted an observational in Long-term warfarin therapy (n=12). Warfarin therapy vs. Sex-matched controls was evaluated on Variation of prothrombin times and international normalized ratio (INR) over 24 hours (p=≤0.03). Warfarin therapy was associated with significant diurnal variations in prothrombin time and INR (p≤0.03), with a mean peak-to-trough difference of 1.8 ± 0.9 seconds.
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