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* From the Clinical Epidemiology Program, Ottawa Health Research Institute, Ottawa, ON, Canada.
Correspondence to: Carl van Walraven, MD, Clinical Epidemiology Program, Ottawa Health Research Institute, C405, Ottawa Hospital, Civic Campus, 1053 Carling Ave, Ottawa, ON, K1Y 4E9 Canada; e-mail: carlv{at}ohri.ca
Abstract
Background: For patients receiving therapy with oral anticoagulants (OACs), the proportion of time spent in the therapeutic range (ie, anticoagulation control) is strongly associated with bleeding and thromboembolic risk. The effect of study-level factors, especially study setting, on anticoagulation control is unknown.
Objectives: Describe anticoagulation control achieved in the published literature. We also used metaregressive techniques to determine which study-level factors significantly influenced anticoagulation control.
Studies: All published randomized or cohort studies that measured international normalized ratios (INRs) serially in anticoagulated patients and reported the proportion of time between INRs ranging from 1.8 to 2.0 and 3.0 to 3.5.
Results: We identified 67 studies with 123 patient groups having 50,208 patients followed for a total of 57,154.7 patient-years. A total of 68.3% of groups were from anticoagulation clinics, 7.3% were from clinical trials, and 24.4% were from community practices. Overall, patients were therapeutic 63.6% of time (95% confidence interval [CI], 61.6 to 65.6). In the metaregression model, study setting had the greatest effect on anticoagulation control with studies in community practices having significantly lower control than either anticoagulation clinics or clinical trials (–12.2%; 95% CI, –19.5 to –4.8; p < 0.0001). Self-management was associated with a significant improvement of time spent in the therapeutic range (+7.0%; 95% CI, 0.7 to 13.3; p = 0.03).
Conclusions: Patients who have received anticoagulation therapy spend a significant proportion of their time with an INR out of the therapeutic range. Patients from community practices showed significantly worse anticoagulation control than those from anticoagulation clinics or clinical trials. This should be considered when interpreting the results of, and generalizing from, studies involving OACs.
Key Words: anticoagulation • deep venous thrombosis • pulmonary embolism
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