Bleeding complications to oral anticoagulant therapy: multivariate analysis of 1010 treatment years in 551 outpatients.

One thousand and ten patient years of oral anticoagulant therapy with vitamin-K-antagonists were reviewed with regard to major bleeding complications. The incidence of bleeding that necessitated hospital admission was 2.7% per year (95% confidence limits, 1.7-3.7%). The major source of bleeding was the alimentary tract, whereas no cases of intracranial bleeding were found. Various factors with potential effects on the bleeding risk were evaluated by multivariate statistical analysis, and the following independent risk factors were identified: age greater than 75 years and hypertension increased the bleeding risk by 10.5% and 4.5%, respectively. Each recorded prothrombin value significantly below the therapeutic range increased the bleeding risk by 3.9%, and each year of treatment increased the risk by 2.0%. These figures may be used to estimate the risk of major bleeding in an individual patient. Current treatment with thiazide diuretics was found to increase the bleeding risk by 5.2%. However, this observation requires further documentation and analysis. Although no lethal episodes of bleeding occurred, the developing field of indications for oral anticoagulant therapy should be considered on the basis of a continuous substantial risk of major bleeding.