Background
Prevention of blood clots, medically known as venous thromboembolism (VTE), is a key patient safety priority for hospitals. VTE includes both deep-vein thrombosis (DVT) and pulmonary embolism (PE), and the risk of developing VTE is highest following major surgery or injury, or when you have heart failure, cancer or a heart attack. Medicines can help prevent blood clots from forming or can dissolve vein blockages. Without treatment, VTE can damage the body’s tissues or organs and a PE can cause death.
All adult patients admitted to hospital need to be risk assessed for VTE according to the criteria set out in the NICE guidance, so that preventative treatments can be given. The VTE risk assessment has been included as a National Quality Requirement in the NHS Standard Contract since 2014/15. This requires acute providers to undertake risk assessments for at least 95% of inpatients each month.
Here we look at how the proportion of inpatients risk assessed for VTE has changed over time. We also examine how deaths from VTE within 90 days of discharge from hospital have changed over time, and how the UK’s post-operative DVT rate compares internationally.
NHS England and NHS Improvement paused data collection and publication for some of their performance statistics due to Covid-19, including VTE risk assessment. The latest data presented here is from Q3 2019/20 (October to December 2019).
Deaths from blood clots after leaving hospital
This indicator measures deaths related to VTE within 90 days post discharge from hospital – a key measure of patient safety. Between 2007/08 and 2019/20, the rate patients who were admitted to hospital with any cause and died from a VTE-related event within 90 days post discharge from hospital decreased from 72 to 62 deaths per 100,000 adult hospital admissions. The absolute number of VTE-related deaths within 90 days post discharge from hospital increased by 13%, from 8,025 in 2007/08 to 9,030 in 2019/20 (data not shown), but the total number of adult hospital admissions increased by 32%, and so the rate of VTE-related deaths decreased.
In 2020/21, the rate of VTE-related deaths within 90 days post discharge from hospital increased considerably to 99 deaths per 100,000 hospital admissions. Between 2019/20 and 2020/21, the number of VTE-related deaths increased by 21% to 10,884, while the total number of adult hospital admissions decreased by 25% to just less than 11 million. A published study found an increased risk of deep vein thrombosis up to three months after Covid-19 infection, and pulmonary embolism up to six months.
Risk assessments for the prevention of blood clots
Since quarter 2 (Q2) of 2010/11, there has been an increase in the proportion of adult inpatients aged 18 and over admitted to NHS-funded acute care (NHS trusts, NHS foundation trusts and independent sector providers) who are risk assessed for venous thromboembolism (VTE). The 95% target was introduced in 2013/14 as part of the national VTE CQUIN goal, and the 95% threshold has been exceeded since 2013/14 Q1.
From April 2019, the target was expanded to include all inpatients aged 16 and over, so rates pre- and post-2019/20 Q1 are not comparable, although the target has been exceeded in both time periods. In 2019/20 Q3, the proportion of adult inpatients who were risk assessed for VTE on admission to hospital was 95.3% for acute providers and 97.6% for independent sector providers.
International comparisons of deep vein thrombosis
Between 2011 and 2020, the post-operative DVT rate in the UK decreased by 11% from 240 per 100,000 hospital discharges to 215 per 100,000 hospital discharges. For each year, the UK rate was lower than the average of all countries that reported data. However, in 2021, the UK had the highest rate of DVT (352) when compared to the eight other countries that reported data. In 2022, it increased to 377 per 100,000 hospital discharges. The average DVT rate between 2009 and 2022 is lowest for the Netherlands and Portugal, and highest for Australia and France.
The OECD's Health at a Glance 2021 suggests that some of the observed variations in DVT rates may be due to differences in diagnostic practices across countries. For example, routine ultrasound screening can significantly increase the detection of DVT. Furthermore, caution is needed in interpreting the extent to which the data accurately reflects international differences in patient safety rather than differences in the way that countries report, code and calculate rates of adverse events. Higher rates may indicate more developed safety monitoring systems and a stronger patient safety culture.
About this data
NHS England data:
The data presented relates to the proportion of adult hospital admissions admitted during the analysis period who are risk assessed for VTE on admission to hospital according to the Department of Health and Social Care/NICE National VTE Risk Assessment Tool. All providers of NHS-funded acute hospital care (including foundation and non-foundation trusts and independent sector providers) are required to complete the data collection, which was mandated in June 2010. From April 2019 onwards, the information was collected for patients aged 16 and over in England; prior to this it was collected for patients aged 18 and over.
From April 2017 to March 2020 the information was published by NHS Improvement.
The VTE data collection and publication is currently paused to release capacity in providers and commissioners to manage the Covid-19 pandemic.
NHS Digital data:
This indicator measures the number of adults (19 years or over) who were admitted to hospital for any reason (not just episodes where VTE had been diagnosed) and subsequently died up to 90 days post-discharge according to the Medical Certificate of Cause of Death (MCCD) and where VTE was one of the conditions leading to, or directly causing death. This is measured per 100,000 adult hospital admissions.
OECD data:
Definitions and comparability for the international indicator are taken directly from the OECD report Health at a Glance 2021: OECD indicators. Detailed information about the definitions and the source and methods for each country can be found here.
The surgical admission-based method uses unlinked data to calculate the number of discharges with ICD codes for deep vein thrombosis in any secondary diagnosis field, divided by the total number of discharges of patients aged 15 and older.
A fundamental challenge in international comparison of patient safety indicators centres on differences in the underlying data. Variations in how countries record diagnoses and procedures and define hospital admissions can affect calculation of rates. In some cases, higher adverse event rates may signal more developed patient safety monitoring systems and a stronger patient safety culture rather than worse care. There is a need for greater consistency in reporting of patient safety across countries and significant scope exists for improved data capture within national patient safety programmes.