low molecular weight heparin and thromboembolism

Last reviewed 04/2020

Low molecular weight heparin is safe and effective in the treatment of deep venous thrombosis (1,2):

  • 64% of patient treated with LMWH and 50% treated with unfractionated heparin showed reduction in DVT size
  • 6% of LMWH-treated patients showed increasing thrombus size versus 12% treated with unfractionated heparin
  • longterm mortality is reduced from 8.1% in the unfractionated group to 4.3% in the LMWH group
  • LMWH has been shown to be as effective as unfractionated heparin in thromboembolic disease whether or not there is pulmonary embolism

A meta-analysis has concluded that, in patients with acute venous thromboembolism, fixed dose subcutaneous low molecular weight heparin is more effective at reducing the incidence of symptomatic recurrent venous thromboembolism, major haemorrhage, and all cause mortality, than adjusted dose unfractionated heparin (3).

However note that a randomised open-label trial of 708 patients aged 18 years or older with acute venous thromboembolism revealed that fixed-dose subcutaneous unfractionated heparin was as effective and safe as low-molecular-weight heparin in patients with acute venous thromboembolism and is suitable for outpatient treatment (4).


  1. Weitz, JI. Low-molecular-weight heparins. NEJM 1997; 337: 689-698.
  2. The Columbus Investigators. Low-molecular-weight heparin in the treatment of patients with venous thromboembolism. NEJM 1997; 337: 657-62.
  3. van Dongen CJ et al. Fixed dose subcutaneous low molecular weight heparins versus adjusted dose unfractionated heparin for venous thromboembolism. Cochrane Database Syst Rev 2004;(4): CD001100.
  4. Kearon C et al. Comparison of fixed-dose weight-adjusted unfractionated heparin and low-molecular-weight heparin for acute treatment of venous thromboembolism. JAMA. 2006 Aug 23;296(8):935-42.