Variations of prothrombin time and international normalized ratio in patients treated with warfarin

Prothrombin time is a standard screening test to monitor patients treated with oral anticoagulants. We hypothesize that INR measurements will not vary a lot within a given day in a given patient. The present study was thus conducted to compare the change of the international normalized ratio (INR) of prothrombin time (PT) within 1 day in patients treated with warfarin. Thirty such patients and nineteen healthy controls were enrolled into this study. PT was performed in four time points of a day in all subjects, two in the morning and two in the afternoon. The four INR values obtained were compared with each other to find little change in the series of time either in patients or in healthy controls. Neither were they affected by renal function, liver function, sex, age, hemoglobin, white cell count, platelet, treatment duration of warfarin, or alcoholic drinking. INR could be measured in any time of a day to have values equally valuable in clinical use.