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This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.

Continuing to take low molecular weight heparin for two to four weeks after major abdominal surgery significantly reduces the risk of developing a dangerous blood clot.

A review of seven studies, mainly in cancer surgery, has found that 13% of patients who received anticoagulant treatment only during their hospital stay developed a clot in the deep veins or lungs, compared with 5% of those who continued with the treatment beyond discharge. There was no increased risk of bleeding complications with prolonged treatment.

This update to a Cochrane review first published in 2009 included three new randomised controlled trials, from Italy, Denmark and Japan, boosting the overall number of participants to 1,728.

The quality of the evidence in this review was moderate overall. The results are consistent with previous studies and strengthen the case for prolonged anticoagulation in an area where there is some uncertainty and variation in practice.

Why was this study needed?

Patients recovering from major abdominal and pelvic surgery are at increased risk of developing venous thromboembolism (VTE), a blood clot in the deep veins or lungs. This risk has been estimated at between 19% and 29% in the most vulnerable patients and is thought to contribute significantly to post-surgery deaths in cancer patients.

While we know that treatment with low molecular weight heparin (LMWH) in hospital is effective, around a third of dangerous blood clots occur after the patient has been discharged from hospital. A 2009 UK prospective study found that the risk of VTE remained 10 to 50 times greater 7 to 12 weeks following inpatient surgery.

We don’t know how long after surgery it is appropriate to continue anticoagulants.

This study sought to evaluate the efficacy and safety of prolonged treatment with heparin for at least 14 days after abdominal or pelvic surgery.

What did this study do?

This systematic review and meta-analysis pooled the results of seven randomised controlled trials, with a total of 1,728 patients. The studies compared prolonged treatment with heparin for 14-28 days, with a shorter duration of treatment during hospital stay only. This review excluded studies where other anticoagulant drugs or devices, such as compression stockings, were evaluated.

Five studies included only people with cancer. Patients in six studies underwent open surgery. In one study, they underwent minimally invasive abdominal surgery. VTEs were confirmed using venograms or compression ultrasound.

Some limitations are noted, including variations in study design and to what extent trials were blinded. One trial received editorial support from a pharmaceutical company.

Overall, the quality of evidence, scale of the review and consistency of the findings indicate these results are reliable.

What did it find?

  • Those who received heparin treatment for up to 28 days after surgery had reduced risk of VTE. The incidence was 5.3% in the patients receiving prolonged anticoagulation, compared with 13.2% in the control group (odds ratio [OR] 0.38, 95% confidence interval [CI] 0.26 to 0.54).
  • When only the six studies involving open surgery were looked at, the results were similar, with 6.0% of the intervention group and 13.8% in the control group developing VTE (OR 0.42, 95% CI 0.29 to 0.60).
  • There was no difference in the incidence of bleeding between the intervention group, affecting 3.4% compared with 2.8% of the control group up to three months after surgery (OR 1.10, 95% CI 0.67 to 1.81).
  • There was no difference in death rate at 3.9% of the intervention group and 3.8% of the control group (OR 1.15, 95% CI 0.72 to 1.84).

What does current guidance say on this issue?

NICE states in its guideline (NG89) that following abdominal surgery, patients whose risk of VTE outweighs their risk of bleeding should have VTE prophylaxis for a minimum of seven days.

NICE recommends that following major abdominal cancer surgery clinicians should consider extending VTE prophylaxis for up to 28 days taking into account individual patient risks.

What are the implications?

These results strengthen the existing evidence and support the current clinical practice guidelines issued by NICE. However, this study looked only at low molecular weight heparin, and there are alternative newer anticoagulants.

The newer oral anticoagulants, removing the need for daily injection, may help to increase the use of anticoagulation at home, but further studies would be needed to assess them for this indication.

Citation and Funding

Felder S, Rasmussen MS, King R et al. Prolonged thromboprophylaxis with low molecular weight heparin for abdominal or pelvic surgery. Cochrane Database Syst Rev. 2019;(8):CD004318.

This review was carried out by the Cochrane Colorectal group, which receives funding from the Danish government.



NICE. Venous thromboembolism in over 16s: reducing the risk of hospital-acquired deep vein thrombosis or pulmonary embolism. NG89. London: National Institute for Health and Care Excellence; updated 2019.

Sweetland S, Green J, Liu B et al. Duration and magnitude of the postoperative risk of venous thromboembolism in middle aged women: prospective cohort study. BMJ. 2009;339:b4583.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre


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