Fixed-Dose Unfractionated Heparin vs Low-Molecular-Weight Heparin for Venous Thromboembolism

Abstract

To the Editor: Dr Kearon and colleagues compared the use of fixed-dose, weight-adjusted unfractionated heparin and low-molecular-weight heparin for acute venous thromboembolism (VTE). One of the key findings was the small risk of major bleeding at 10 days, although there was a non– statistically significant difference at 3 months (1.7% for the unfractionated heparin group vs 3.4% for the low-molecularweight heparin group). We believe that the definitions of bleeding are too heterogeneous and that further clarification of the underlying etiology of the bleeding is required. In this study, bleeding was defined as major if it was clinically overt and associated with a decrease in hemoglobin level of at least 2.0 g/dL, involved a need for transfusion of 2 or more units of red blood cells, or involved a critical site (eg, retroperitoneal, intracranial). These are less stringent criteria than the TIMI classification, which requires a decrease in hemoglobin of more than 5.0 g/dL (implying gastrointestinal loss) to satisfy this criterion. Furthermore, the authors do not give a definition of minor bleeding, which, while not as serious, is nevertheless common. The incidence of gastroduodenal lesions in VTE was about 16% in a study of 155 patients (P=.005); this included peptic ulcers and diffuse erosions (albeit largely asymptomatic). This is important when considering the increased mortality from gastrointestinal bleeding with superimposed comorbidity that will be experienced by many patients with VTE. While validated risk index tools exist, further elucidation of bleeding etiology and the appreciation of these risks in clinical and research settings need to be borne in mind.