Skip to content
View commentaries on this research

This is a plain English summary of an original research article

Reminders to assess clotting risk result in more patients being given appropriate anti-clotting measures in hospital. Computer alerts, in particular, are linked to better choice of prophylaxis and fewer blood clots in veins.

Clots in deep leg veins or the lungs are common when people are bedbound in hospital. This updated Cochrane review assessed interventions aiming to increase the use of appropriate preventive measures such as anti-clotting drugs or mechanical measures, including stockings, for people at risk.

Analysis of three trials which looked specifically at alerts, either computerised or delivered by a healthcare professional, found the proportion of patients receiving anti-clotting measures increased by 21 percentage points, from 18% to 39%. The proportion having symptom-causing clots within three months reduced from 5.5% to 3.5%. Multifaceted interventions, most including education and audit, were much less effective.

The latest figures show that 96% of adults do have a clotting risk assessment on admission to NHS hospitals. Rates do vary, and alerts could be useful for those hospitals which fall below the recommended target of 95%.


Why was this study needed?

Hospitalised medical and surgical patients are at a 50% higher risk of developing blood clots in veins compared to adults in the general community. Venous clots, including clots that travel to the lungs, are a common cause of preventable hospital mortality.

Mechanical interventions such as anti-clotting stockings and preventive drugs are, on balance, effective and safe if used as recommended to prevent clots. However, the assessment of risk can be complex, and it is not always considered in day-to-day practice.

This review aimed to determine the effectiveness of different measures to encourage appropriate use of clot-preventing treatments in hospitals.


What did this study do?

This update to a previous Cochrane review included 13 RCTs involving 35,997 adult patients. It compared interventions to increase the use of anti-clotting measures with standard care alone or another intervention.

It was not possible to provide summary statistics for two studies. Six studies looked at alerts (computer or healthcare professional-delivered). A further five studies looked at pre-printed prescription forms, education programmes, audit and feedback, or combinations of these (multifaceted interventions). The content of standard care was not described. None of the included studies took place in the UK (most were in the US, with two in Europe).

The review’s authors report low-to-moderate certainty in the results overall. This was largely because some trials did not provide enough detail on their methods to rule out bias.


What did it find?

  • Results from three studies (5,057 patients) found that alert-based interventions increased the proportion of patients who received clot-preventing measures (mechanical or drug prophylaxis) by 21% compared with standard care (39% received treatment with alerts vs 18% with standard care; risk difference [RD] 0.21, 95% confidence interval [CI] 0.15 to 0.27; low certainty evidence). The studies showed some inconsistency in results, with computerised alerts tending to show larger effects.
  • Results from three other studies found that alerts also increased the proportion of patients who received appropriate clot-preventing measures by 16% (46% received appropriate treatment with alerts vs 30% with standard care; RD 0.16, 95% CI 0.12 to 0.20; three studies, 1,820 patients, moderate certainty evidence).
  • Alerts reduced the proportion of patients who developed a symptom-causing clot in a vein within three months of the intervention from 5.6% to 3.5% (relative risk 0.64, 95% CI 0.47 to 0.86; three studies, 5,353 participants, low certainty evidence).
  • Single studies found that an educational intervention and pre-written prescription aids did not increase the use of anti-clotting treatments compared with standard care.
  • A small benefit from multifaceted interventions in the proportion of patients who received clot-preventing measures appeared to be attributable to a study where the multifaceted intervention contained an alert.


What does current guidance say on this issue?

A NICE guideline (NG89) on reducing the risk of hospital-acquired deep vein thrombosis or pulmonary embolism in those aged over 16 recommends conducting a risk assessment as soon as possible after admission to hospital or by the time of the first consultant review. It recommends using a tool (such as the Department of Health’s venous thromboembolism risk assessment tool) which is published by a national UK body, professional network or peer-reviewed journal.

The guideline also makes specific recommendations on when medication is appropriate or when other preventive measures such as anti-clotting (anti-embolism) stockings and early mobilisation may be preferred.


What are the implications?

This review adds weight to the efforts at implementation such as reminder systems that now exist in the NHS. National measures to reduce hospital-acquired clots have been in place in the NHS since 2010. Since then, there has been a 15% reduction in deaths from clots within 90 days of hospital discharge.

The NHS Standard Contract requires that at least 95% of adults should be risk assessed on admission. In the first three months of 2019, 96% of adults admitted to NHS acute care hospitals were assessed for clotting risk according to NHS Improvement data.

There is nevertheless unexplained variation, and about 23% of NHS providers report thrombosis risk assessment rates below 95%. For these providers, increased use of alerts could improve process and outcome.


Citation and Funding

Kahn SR, Diendere G, Morrison DR et al. Effectiveness of interventions for the implementation of thromboprophylaxis in hospitalised patients at risk of venous thromboembolism: an updated abridged Cochrane systematic review and meta-analysis of randomised controlled trials. BMJ Open 2019; 9 (5) pe024444.

This review was funded by the Canadian Institutes for Health Research. The authors are supported by the Canadian Government’s Canada Research Chair scheme, the Canadian Venous Thromboembolism Clinical Trials and Outcomes Research (CanVECTOR) Network, and the Fonds de recherche du Québec - Santé (Quebec Foundation for Health Research).



Department of Health. Risk assessment for venous thromboembolism (VTE). London: Department of Health; 2010.

Hunt BJ. Preventing hospital associated venous thromboembolism. BMJ 2019;365:l4239.

Kahn SR, Morrison DR, Diendéré G, et al. Interventions for implementation of thromboprophylaxis in hospitalized patients at risk for venous thromboembolism. Cochrane Database Syst Rev 2018; 4: CD008201.

NHS Improvement. Venous thromboembolism risk assessment data collection: Quarter 4 2018/19 (January to March 2019). London: NHS Improvement; 2019.

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


  • Share via:
  • Print article
Back to top