PT  - JOURNAL ARTICLE
AU  - Natalie Oake, MSc
AU  - Alison Jennings, MA
AU  - Alan J. Forster, MD MSc
AU  - Dean Fergusson, PhD
AU  - Steve Doucette, MSc
AU  - Carl van Walraven, MD MSc
TI  - Anticoagulation intensity and outcomes among patients prescribed oral anticoagulant therapy: a systematic review and meta-analysis
AID  - 10.1503/cmaj.080171
DP  - 2008 Jul 29
TA  - Canadian Medical Association Journal
PG  - 235--244
VI  - 179
IP  - 3
4099  - http://www.cmaj.ca/content/179/3/235.short
4100  - http://www.cmaj.ca/content/179/3/235.full
SO  - CMAJ2008 Jul 29; 179
AB  - Background: Patients taking oral anticoagulant therapy balance the risks of hemorrhage and thromboembolism. We sought to determine the association between anticoagulation intensity and the risk of hemorrhagic and thromboembolic events. We also sought to determine how under-or overanticoagulation would influence patient outcomes. Methods: We reviewed the MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials and CINAHL databases to identify studies involving patients taking anticoagulants that reported person-years of observation and the number of hemorrhages or thromboemboli in 3 or more discrete ranges of international normalized ratios. We estimated the overall relative and absolute risks of events specific to anticoagulation intensity. Results: We included 19 studies. The risk of hemorrhage increased significantly at high international normalized ratios. Compared with the therapeutic ratio of 2–3, the relative risk (RR) of hemorrhage (and 95% confidence intervals [CIs]) were 2.7 (1.8–3.9; p < 0.01) at a ratio of 3–5 and 21.8 (12.1–39.4; p < 0.01) at a ratio greater than 5. The risk of thromboemboli increased significantly at ratios less than 2, with a relative risk of 3.5 (95% CI 2.8–4.4; p < 0.01). The risk of hemorrhagic or thromboembolic events was lower at ratios of 3–5 (RR 1.8, 95% CI 1.2–2.6) than at ratios of less than 2 (RR 2.4, 95% CI 1.9–3.1; p = 0.10). We found that a ratio of 2–3 had the lowest absolute risk (AR) of events (AR 4.3%/yr, 95% CI 3.0%–6.3%). Conclusions: The risks of hemorrhage and thromboemboli are minimized at international normalized ratios of 2–3. Ratios that are moderately higher than this therapeutic range appear safe and more effective than subtherapeutic ratios.