High-Dose Unfractionated Heparin in Overweight and Obese Patients

Study Questions:

Does high-dose unfractionated heparin safely and effectively prevent venous thromboembolism (VTE) in overweight and obese patients?


This was a single-center retrospective observational cohort study at a large academic medical center. Overweight or obese adult patients admitted to the hospital between January 1, 2013, and August 31, 2014, who received unfractionated heparin for VTE prophylaxis were included. The primary outcome was incidence of VTE, and the secondary outcome was the incidence of major and minor bleeding.


A total of 1,335 adults were included in the analysis, including 751 patients who received high-dose (7,500 units every 8 hours) unfractionated heparin and 584 patients who received low-dose (5,000 units every 8 hours) unfractionated heparin. Patients were subdivided into 4 groups based on their body mass index (BMI):

  • Overweight (25-29.9 kg/m2)
  • Obese class I (30-34.9 kg/m2)
  • Obese class II (35-39.9 kg/m2)
  • Obese class III (>40 kg/m2)

Baseline differences among these groups included the following:

  • Major surgery was more common in the low-dose obese class II and III groups.
  • The high-dose obese class I group was more likely to have major surgeries.
  • Heart failure was more common in the high-dose obese class III group.

Although the sample size obtained was short of the initial goal, the overall incidence of VTE was similar between the high-dose and low-dose groups (3 vs. 1.5%, respectively; p = 0.14). Additionally, no significant difference was found after adjusting for BMI. Patients receiving high-dose unfractionated heparin were, however, more likely to have a >2 g/dl drop in hemoglobin during any 24-hour period than those receiving low-dose unfractionated heparin (10 vs. 7%, respectively; p < 0.01) and receive >2 units of packed red blood cells (11 vs. 8%, respectively; p = 0.04). These findings were also significant for obese class II and III groups, indicating an increased bleeding risk among these individuals who were also receiving high-dose unfractionated heparin. It is important to note that antiplatelet use was higher among high-dose versus low-dose obese class III patients; however, a multivariable regression analysis found that this was not significant. High-dose unfractionated heparin was associated with a longer length of stay across all BMI groups, but no difference in mortality was observed.


High-dose unfractionated heparin did not reduce the incidence of VTE in a cohort of hospitalized overweight and obese patients. However, high-dose unfractionated heparin was associated with an increased risk of major bleeding, particularly in those patients with a BMI >40 kg/m2 who were concomitantly receiving aspirin.


The findings from this study are inconsistent with those observed in the bariatric population, where high-dose unfractionated heparin has been shown to reduce the incidence of VTE without a major increase in bleeding. Further study with a large sample size across multiple centers is warranted to fully explore and validate these results.

Clinical Topics: Anticoagulation Management, Heart Failure and Cardiomyopathies, Pulmonary Hypertension and Venous Thromboembolism, Vascular Medicine, Anticoagulation Management and Venothromboembolism, Acute Heart Failure

Keywords: Aspirin, Bariatrics, Body Mass Index, Heart Failure, Hemorrhage, Heparin, Obesity, Overweight, Venous Thromboembolism

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