The World Health Organization estimates that worldwide, more than 300 million persons are obese . Obesity and malignancy are risk factors for development of venous thromboembolism (VTE) . Patients with cancer may be cachexic. Therefore, any study of VTE treatment is likely to enrol patients who are at either end of the weight spectrum. Previously, little information was known regarding how such patients were treated. The most concrete clinical trial data we had was that from Merli et al.  who reported in a post hoc analysis that there was a ‘non-significant’ trend toward an increased rate of VTE recurrence with once vs. twice daily administration of enoxaparin in patients who were obese. Information on dosing low-molecular-weight heparin (LMWH) in patients who are obese is scarce [4,5]. In this issue of the Journal, Barba et al.  report the results of VTE treatment strategies and 15-day outcomes in more than 8000 patients from RIETE, an ongoing Spanish registry. In their report, anticoagulant treatment strategies, VTE recurrence, major and total bleeding were reported in two important sub groups of patients: those weighing <50 kg (n = 169) and those weighing >100 kg (n = 294). Outcomes were compared with each other and a group of patients weighing 50–100 kg. This study from the RIETE investigators was notable for the following findings.
- 1Initial LMWH therapy was chosen for almost all patients (95% of patients weighing <50 kg and 82% of patients weighing >100 kg).
- 2An unacceptable number of patients weighing <50 kg (54%) received >200 IU/kg day−1 of LMWH. (The usual dose is 150–200 IU kg−1 day−1).
- 3Only two patients weighing >100 kg received >200IU kg−1 day−1. However 74% received <175IU kg−1 day−1. As the authors state, this may be secondary to an artificial dosing cap in place at individual institutions.
- 4There was no difference in recurrent VTE and major bleeding between patient groups. Body weight was not associated with an increased risk for major bleeding.
- 5Major bleeding was lower in patients initially treated with LMWH compared with unfractionated heparin (UFH).
- 6In unadjusted analysis, the total bleeding rate was higher in patients weighing <50 kg.