All patients admitted to hospital in England should be risk assessed to ascertain their individual risk of thrombosis and bleeding. This vital assessment informs whether thromboprophylaxis is required. The simultaneous assessment of both thrombosis and bleeding allows clinicians to make considered decisions about how best to maintain haemostasis to ensure that patient safety is optimised. This careful balance between bleeding and clotting can fluctuate frequently in acutely unwell patients, emphasising the need for reassessment as clinical condition changes.

Risk assessment is a collaborative process to be performed with the patient. This offers an ideal opportunity to impart information about the risk of VTE as well as signs and symptoms and what action to take should they develop. The National target for VTE risk assessment in England is currently 95% although it is important that organisations aim to risk assess all adult admissions.

The National VTE Prevention Programme

The National VTE Prevention Programme launched in England in 2010. The principal aim was to reduce morbidity and mortality associated with preventable hospital-associated venous thromboembolism (VTE). An innovative, comprehensive and systematic approach was taken underpinned by the introduction of a financially incentivised mandatory, documented VTE risk assessment on admission to hospital (target 90% risk assessment rate at launch; Institute for Innovation and Improvement, 2010). This was supported by thromboprophylaxis guidance published by NICE with a quality standard outlining best practice (NICE 2010a,b). Additional initiatives include the National VTE Exemplar Centre Network, a national VTE prevention website (now decommissioned) and an electronic learning resource for VTE prevention.

Lower Limb Immobilisation

The need for thromboprophylaxis in this patient group (particularly in patients being treated conservatively in the outpatient setting) remains a controversial topic. The absolute incidence of symptomatic VTE appears to be low and there is limited evidence to recommend routinely giving thromboprophylaxis. The KAF study (Selby et al, 2014), a multicentre prospective cohort study to define the prevalence of symptomatic VTE in patients with a tibial, fibular, or ankle fracture (treated non-operatively) or a patellar or foot fracture (treated operatively or conservatively) found the incidence of symptomatic VTE to be 0.6% without thromboprophylaxis.

A Cochrane review (2017) concluded that there is moderate quality evidence to support the use of LMWH in outpatients with lower limb immobilisation (when compared with no prophylaxis or placebo) and despite no significant difference in PE rates between LMWH and control groups (low quality evidence), there were fewer symptomatic VTEs in the LMWH groups.

This was based on a meta-analysis and the eight studies included differed widely in many respects e.g. different types and doses of LMWH, different risk groups (e.g. non-operative, operative) as well as primary outcomes (e.g. symptomatic vs asymptomatic DVT).

More recent data suggests that LMWH given throughout the period of immobilisation may not be effective for the prevention of symptomatic VTE (POT-CAST trial, van Andrichem et al, 2017). Notably, although patients managed both conservatively and surgically were included in this trial, patients with a history of VTE were excluded, as were pregnant patients and those with multiple traumatic injuries.

The latest NICE guidelines (NG89 2018) state:

“Consider pharmacological VTE prophylaxis with LMWH or fondaparinux sodium for people with lower limb immobilisation whose risk of VTE outweighs their risk of bleeding. Consider stopping prophylaxis if lower limb immobilisation continues beyond 42 days.”

Practice varies widely across the UK and many different risk assessment tools are in use at various hospitals. NICE guidelines (NG89 2018) recommend that risk assessment should be performed “using a tool published by a national UK body, professional network or peer-reviewed journal”. Importantly, there is no validated risk assessment tool for this patient group.

In summary, patients deemed to be high risk of VTE should be considered for thromboprophylaxis during lower-limb immobilisation but the question of how this group should be defined remains unresolved.


VTE risk assessment for all pregnant women should occur in early pregnancy and then again in labour or immediately after delivery. Some women deemed to be at high thrombotic risk may require thromboprophylaxis throughout pregnancy and for 6 weeks post-partum. The Royal College of Obstetricians and Gynaecologists (2015) provides guidance for clinicians in reducing the risk of venous thrombosis in pregnancy and the puerperium.

The Royal College of Obstetricians and Gynaecologists


Some cancers and cancer treatments are associated with an increased risk of thrombosis. Patients should be risk assessed and considered for thromboprophylaxis in line with NICE (2018) guidance.

Adult Inpatient Tool (Department of Health)

Risk assessment for Venous Thromboembolism (VTE)

Obstetric Tool (RCOG)

Obstetric thromboprophylaxis risk assessment and management

VTE Risk - Patient information

Blood clots can be very serious and need to be treated quickly. Staying healthy and active can help prevent them.