These studies validate the belief that increased provider continuity is associated with improved patient outcomes and satisfaction. Further research is required to determine whether information or management continuity improves outcomes.

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O ral anticoagulant therapy is essential for the treatment and prevention of many thromboembolic disorders. Since anticoagulants can cause serious adverse events, 1-3 physicians monitor the international normalized ratios of patients taking these drugs to ensure that their ratios fall within a target range.An international normalized ratio of 2-3 is the most common target range. Results of previous studies revealed an increased risk of bleeding among patients whose ratios exceeded 4, an increased risk of stroke among patients whose ratios were 1.5-2 and a decreased risk of stroke at a ratio of 2.4. 4,5 However, the evidence supporting the range of 2-3 has some deficiencies. We sought to determine whether the risk of hemorrhagic and thromboembolic events is minimized at an international normalized ratio of 2-3 among patients taking anticoagulants. In addition, it has been observed that patients spend more time with a ratio below 2 than above 3.6,7 The impact of such systematic underanticoagulation on patient outcomes is unknown. We sought to determine the effect of under-or overanticoagulation on the risk of thromboemboli and hemorrhage. Methods Data sourcesWe searched MEDLINE (1966MEDLINE ( -2006 for potentially pertinent studies. We then modified our strategy to include EMBASE (1980EMBASE ( -2006, the Cochrane Central Register of Controlled Trials (1980Trials ( -2006 and CINAHL (1982CINAHL ( -2006 databases. We manually searched references in the Science Citation Index. Our search strategy is outlined in Appendix 1 (available at www.cmaj.ca/cgi/content/full/179/3/235/DC2). Study selection

DOI:P atients taking anticoagulants orally over the long term have international normalized ratios (INRs) that fall outside the individual therapeutic range more than one-third of the time.1 Improved anticoagulation control reduces hemorrhagic and thromboembolic event rates. 2,3 Many studies have shown that such event rates are higher when patients' INRs are outside the therapeutic range.4-11 A study that systematically measures the proportion of hemorrhages and thromboemboli that occur when INRs are above and below the therapeutic range, respectively, will help both physicians and policy-makers gauge the potential effect of improved anticoagulation control. In our investigation, we measured and analyzed these proportions. MethodsWe identified pertinent citations in English in the MEDLINE and EMBASE (1980EMBASE ( -2006 databases using the search strategy outlined in Appendix 1. This strategy combined medical subject headings and keywords related to anticoagulation (e.g., anticoagulants, warfarin) and to hemorrhages and thromboemboli (e.g., cerebrovascular accident, bleed). We retrieved the full text of articles for further review if the title or abstract suggested that patients taking anticoagulants were studied and data on hemorrhages or thromboemboli were reported. Studies were included in our review if the majority of patients taking anticoagulants orally had an INR range with a lower limit between 1.8 and 2 and an upper limit between 3 and 3.5, and the INR at the time of the hemorrhagic or thromboembolic event was recorded; these limits represent the most common therapeutic ranges for patients taking oral anticoagulants. All citations and studies were reviewed for inclusion by a single author (N.O.). We considered all major hemorrhages (i.e., those that required hospital admission, a transfusion or surgery, or that reduced hemoglobin levels by ≥ 20 g/L) and thromboemboli (stroke, myocardial infarction, venous thromboembolism or systemic emboli, confirmed by objective tests). We excluded patient groups taking anticoagulants by mouth with concomitant antiplatelet therapy, because their risk of hemorrhagic and thromboembolic events is considerably higher than the risks of patients taking anticoagulants alone. 12,13From each study, we abstracted the total number of major hemorrhages and thromboemboli that could be assigned to particular INR ranges. Some studies assigned events to INRs based on measurements taken at the time of the event or at hospital admission, whereas others used measurements made beforehand to approximate the INR at the time of the event. We grouped the events into 3 INR ranges: below, DOI:10.1503/cmaj.061523 Natalie Oake, Dean A. Fergusson, Alan J. Forster, Carl van Walraven Frequency of adverse events in patients with poor anticoagulation: a meta-analysis Background: Patients taking anticoagulants orally over the long term have international normalized ratios (INRs) outside the individual therapeutic range more than one-third of the time. Improved anticoagulation control will reduce hem...

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