Patient preferences for capillary vs. venous INR determination in an anticoagulation clinic: a randomized controlled trial

BACKGROUND: Patients who are receiving warfarin therapy require frequent blood testing to monitor the intensity of anticoagulation. Although previous studies suggest that capillary blood monitoring of the international normalize ratio (INR) is rapid and reliable, patient preferences for the method of blood drawing have not been investigated. METHODS: We performed a randomized controlled trial of patients attending an anticoagulation clinic in which patients were randomly allocated to undergo capillary or venous INR monitoring. Patient satisfaction with the outpatient visit, pain associated with blood drawing, and time spent in the clinic were assessed for each patient. RESULTS: Sixty patients were studied. Using a 10-point visual analogue scale to quantify patient satisfaction (0-very satisfied; 10-very dissatisfied), patients expressed a strong preference for capillary INR monitoring over venous INR monitoring (1.64 vs. 4.45; P < 0.001). Using a 10-point visual analogue scale to quantify pain with blood sampling (0-no pain; 10-very painful), patients who underwent capillary INR testing had less pain than venous INR testing (0.83 vs. 2.23; P < or = 0.004). Patients spent, on average, 33 fewer minutes in the clinic with capillary INR testing than venous INR testing (P < 0.001). DISCUSSION: Our findings support the routine use of capillary blood testing, using a portable monitor, for the management of patients in outpatient anticoagulation clinics.