Patients receiving long-term warfarin therapy prefer INR testing with capillary fingerstick over venous blood testing

Abstract number: P1963

Woods^* K., Schnurr^* T., Kinnon† K., Crowther^* M. A., Mallory† S., Douketis^* J. D.

^*McMaster University, Canada; †St Joseph's Hospital, Canada

Capillary blood systems capable of reliable measurement of the international normalized ratio (INR) are widely used and highly accurate. In anti-coagulation clinics, capillary INR testing has the advantages of speed and ease of use, and has become the preferred method for determining the INR in many centers. However, to our knowledge, no studies have investigated the impact of capillary INR testing on: (a) pain associated with blood drawing, or (b) patient satisfaction with the anti-coagulant clinic visit. We therefore undertook a randomized controlled trial in patients presenting for INR testing and clinical assessment in an outpatient anti-coagulant clinic of a tertiary care teaching hospital. After providing written informed consent, patients were randomly allocated to have INR testing by conventional venapuncture and laboratory INR methods, or capillary INR testing with a portable coagulometer (CoaguChek S, Roche Diagnostics). Variables recorded included patient demographics and the time the patient spent in the clinic. The primary outcome was patient satisfaction, measured using a 10-point visual analog scale at the end of the clinic visit. The discomfort associated with blood drawing was also assessed on a similar scale. We evaluated 70 consecutive eligible patients, of whom 60 provided consent and 30 were allocated to capillary INR testing. Baseline demographics were similar in the two groups. Patients expressed a strong preference for capillary INR determinations. Thus, on the scale of 0 (indicating the ‘best ever’ clinic visit) to 10 (indicating the ‘worst ever’ visit), the mean assessment score in the capillary group was 1.64 (95% CI 0.65–2.64) compared with 4.45 (95% CI: 3.48–5.42) in the venous group (P < 0.001). Patients also reported less pain with capillary than venous INR testing based on a mean visual analog scale score (0.83 vs. 2.23, P = 0.004). INR testing with the capillary system took, on average, 33 min less time than conventional laboratory testing (P = 0.003). We conclude that INR testing using a capillary system is (a) preferred by patients (b) less painful than venous INR testing, and (c) saves, on average 33 min of patient time when performed in an outpatient anti-coagulant clinic. These findings support the routine use of portable INR monitors for the management of patients in an outpatient anti-coagulation clinic.