Patient self-testing is a reliable and acceptable alternative to laboratory INR monitoring

Abstract

SAn ageing population and the continuing expansion of clinical indications for coumadin therapy have increased pressure on hospital anticoagulant clinics. One solution is patient self-testing (PST) of the international normalized ratio (INR) using capillary blood samples on point-of-care coagulation monitors at home. We conducted a prospective study to determine whether patients can achieve accurate INR values through PST, using the CoaguChek S (Roche Diagnostics, Lewes, UK). The main outcome measurements were: comparability of INR values obtained by PST and the hospital laboratory, patient acceptability as assessed by a questionnaire and anticoagulant control. Eighty-four patients [53 men, 31 women; median age 59 years (range 26-83)], receiving long-term oral anticoagulation (warfarin), were recruited from our Anticoagulation Clinic. Patients were randomized to weekly self-testing or continuing 4-weekly hospital laboratory monitoring of INR. Comparison of INRs (n = 234) showed no significant differences between the CoaguChek (median INR 3.02) and laboratory testing (median INR 3.07). There was excellent correlation between the two methods (r = 0.95), with 85% of CoaguChek results within 0.5 INR units of the laboratory method. On four occasions, differences of >1 unit INR were obtained, but in each case the patient's anticoagulation was unstable (INR >4.5 by both methods) and the differences in INR would not have altered patient management. 87% of patients found self-testing straightforward, 87% were confident in the result they obtained and 77% preferred self-testing. We conclude that PST is a reliable alternative to hospital clinic attendance and is acceptable to the majority of suitably trained patients.