ArticlesOral anticoagulation self-management and management by a specialist anticoagulation clinic: a randomised cross-over comparison
Introduction
Oral anticoagulant treatment with vitamin K antagonists, such as warfarin or coumarin derivatives, has been shown to be effective for the prevention and treatment of thromboembolic events in various clinical circumstances.1, 2 Some patients need to be treated with vitamin K antagonists for a long time, even life-long, such as patients with mechanical prosthetic heart valves or patients with recurrent venous thromboembolism due to familial thrombophilia. The biological effect of these compounds—ie, inhibition of the synthesis of vitamin K-dependent coagulation factors-is extremely variable, both interindividually and intraindividually. Factors influencing this variability include fluctuating bioavailability, inconstant dietary vitamin K intake, changes in other drugs that the patient might be taking, and variable binding to plasma proteins.2, 3 To prevent under-treatment or overdosing, regular laboratory control (by means of the prothrombin time, expressed as and referred to throughout this paper as international normalised ratio [INR]) of the intensity of anticoagulation and dose-adjustments are necessary.4 This management of oral anticoagulant therapy is often executed by hospital-based or specialised anticoagulation clinics, such as the “Thrombosis Service” in the Netherlands. Although this type of management is thought to be superior to less well-organised management of oral anticoagulation,5, 6 and despite a strong organisation, laboratory quality control, and automated, computerised dose-adjustments, for many patients the intensity of anticoagulation does not fall within the “therapeutic target range” for long periods.7, 8, 9, 10 Besides, the visits to the anticoagulation clinic are rather time-consuming and, for some patients, inconvenient.
Easy and reliable laboratory devices have become available, which allow the measurement of the prothrombin time (expressed as INR) from one drop of capillary whole blood.11, 12, 13 Application of these devices may allow patient self-testing of the intensity of anticoagulation and self-adjustment of the warfarin dose.14 Self-management of oral anticoagulant therapy may result in a more individualised approach, increased patient responsibility, and enhanced complziance, which may lead to improvement in the regulation of anticoagulation. An additional advantage could be that patients can do the test at home (saving travel and time during working hours) and are less dependent of the anticoagulation clinic. A potential disadvantage of self-management could be a poorer regulation of oral anticoagulant therapy, due to less professional guidance. Also, self-management of oral coagulation may theoretically be associated with increased anxiety of patients or even preoccupation with their disease
Previous studies have shown the feasibility of self-testing and self-management of oral anticoagulation,15, 16, 17, 18, 19 while two investigations showed the potential superiority of self-management over that of general practitioners20, 21. Self-management of anticoagulation has, however, so far not been compared with management by a specialised anticoagulation clinic. The aim of the present study was to directly compare the quality of self-management of oral anticoagulation with conventional care by the Thrombosis Service in the Netherlands in a randomised cross-over study.
Section snippets
Study design
The study was approved by the Institutional Review Board of the Academic Medical Centre of the University of Amsterdam, the Netherlands.
The study was done in two phases. In the first phase a direct comparison was made between self-measurement and self-dosing of vitamin K antagonists and anticoagulation-clinic-based management. The second phase of the study was done as a randomised cross-over study comparing self-management of oral anticoagulation with anticoagulation-clinic management.
In the
Measurement of INR
Venous blood (9 vol) was collected in 3·2% sodium citrate (1 vol) and plasma was obtained by centrifugation at 1800Xg for 20 min. The prothrombin time (PT) was measured in plasma by Tromborel-S reagent (Dade Behring, Leusden, Netherlands, ISI value 1·19) on a Elekra 1600 coagulometer (MLA, Pleasantville, NY). PT values were expressed as an INR according to international convention. Self-measurement of INR was done on capillary blood (obtained by a fingertip puncture, Softclix lancet system) on
Subjective quality of care assessment
A self-perceived assessment of the quality of care was made by patients using a structured questionnaire containing 32 items, which has been described previously.21 This questionnaire measures patients' feelings about oral anticoagulation, general treatment topics, treatment satisfaction, self-efficacy, daily frictions and worries, and social issues. For each category a minimum of 1 point (total dissatisfaction) and a maximum of 6 points (complete satisfaction) could be scored. This assessment
Sample size and statistical analysis
All data are presented as mean (SD). The agreement between self-measurements and laboratory measurements in the initial phase of the study was analysed as previously described.26, 27 The accuracy of the control of anticoagulation was assessed by evaluating the number of INR values within and outside the therapeutic target range and by measuring the length of time of adequate anticoagulation. The time in the therapeutic target range was calculated by means of linear interpolation.28 The number
Feasibility and safety of self-management
In the first phase of the study a direct comparison of INRs (self-measured and measured at the anticoagulation clinic) and warfarin-dosing schemes (self-devised or clinic-based) was made for the 6-week study period. All patients were able to measure the INR at home and to devise a dosing scheme for the next week. There was an acceptable correlation between the self-measured INR and the clinic INR (figure 1). The mean difference between all self-measurements and all clinic measurements was 12·3%
Discussion
Oral anticoagulation with warfarin is an effective measure for the treatment and prevention of arterial and venous thromboembolism. However, the substantial interindividual and intraindividual variation in the biological effect of vitamin K antagonists renders many patients outside the therapeutic target range over long periods of time. This is cumbersome for several reasons. First, clinical studies show that under-coagulation and over-coagulation enhance the risk of adverse clinical
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