One per cent PE risk. One per cent bleed risk. Equal numbers — unequal outcomes

Quality improvement · NHS · Venous thromboembolism

One per cent PE. One per cent bleed. Equal numbers — unequal outcomes

A figure circulates on surgical wards: the risk of pulmonary embolism in hospital inpatients is about one per cent. The risk of catastrophic bleeding from pharmacological thromboprophylaxis is also about one per cent. Equal numbers. A stand-off. Many surgeons — particularly in general surgery — treat that parity as a reason to hesitate, to individualise, to let the VTE assessment form decide.

The arithmetic is seductive. The conclusion is wrong — not because surgeons are careless, but because the two percentages measure different things and cause different harms.

The tension is real in the literature

In pooled randomised data for moderate-risk general surgery, low molecular weight heparin prevents clinical venous thromboembolism in roughly one patient per 150 (number needed to treat ~147). Major haemorrhage attributable to prophylaxis occurs in roughly one per 67 (number needed to harm ~67). On a pure event-count basis, more patients may suffer prophylaxis-related bleeding than avoid thrombosis — in that selected trial population.

That is the evidence behind the worry. It is why some analyses argue chemoprophylaxis should be reserved for groups where clinical VTE risk exceeds roughly three per cent. It is why a surgeon who sees a wound haematoma or a return to theatre blames the heparin.

The ward conversation — one per cent versus one per cent — compresses that literature into a single intuitive dread. Rate parity feels like equipoise. It is not.

Catastrophic bleed and fatal PE are not symmetric

Major bleeding in prophylaxis trials means transfusion, drop in haemoglobin, sometimes reoperation. It is serious. It is not the same as catastrophic bleeding — intracranial haemorrhage, exsanguination, permanent neurological injury. Those outcomes from prophylactic-dose heparin in fit surgical patients are rare. Fatal bleeding at prophylactic dose is a fraction of the major-bleed numerator.

Pulmonary embolism is different. Symptomatic PE carries mortality often quoted around ten to fifteen per cent in hospitalised patients; massive PE kills quickly. The prevented event is frequently life-ending. The caused event, in most cases, is treatable morbidity.

When rates look equal, outcomes do not

	Prophylaxis harm	Untreated PE
Typical event	Transfusion, haematoma, delay	Hypoxia, collapse, death
Catastrophic tail	Uncommon at prophylactic dose	Common enough to fear
Reversibility	Often	Sometimes, if caught

Equal rates do not mean equal stakes. Harm reduction and life-saving logic favour prevention when thrombotic risk is genuine — even if the numerators look similar on a spreadsheet.

"Low VTE risk" is often a form, not a patient

The escape hatch in guidelines is the low-risk patient: fully mobile, short stay, medical admission without immobility. In a contemporary UK acute NHS hospital, that patient is rare.

Medical beds are not filled by people walking the corridor awaiting a taxi. They are filled by hypoxia, sepsis, heart failure, delirium, and frailty collapse. Surgical beds hold patients who have had general anaesthesia — venous stasis, dehydration, tissue injury, inflammatory hypercoagulability — in a population that is older, heavier, and less mobile than a decade ago. Day-case volume has grown, but the biology of operation does not shrink because discharge is earlier.

When a risk assessment tool labels someone "low risk," it often reflects which boxes were ticked, not physiology. The same patient can score differently on different models; recommendations for prophylaxis have ranged from one in ten to nine in ten depending on the tool. Low risk on paper is a weak exception in practice.

For major orthopaedic surgery — hip fracture, arthroplasty, major trauma — the debate barely applies. VTE risk without prophylaxis is among the highest in surgery. The surgeon's question there is timing after neuraxial block and duration post-discharge, not whether clot risk exists.

Narrow exceptions — not broad opt-outs

Day-case surgery does not mean low thrombotic risk. Much hospital-associated VTE is diagnosed after discharge. Procedural catastrophic bleeding in standard day cases is uncommon. Day-case growth widens the surgical pool at risk; it does not create a legion of mobile low-risk patients.

Orthopaedic exceptions are specific: active bleeding, severe thrombocytopenia, neuraxial anaesthesia where prophylaxis must be delayed until safe — not withheld because VTE risk is doubted.

Across medical, surgical, and orthopaedic inpatient wards, the withhold reasons that survive scrutiny are a short list:

• active haemorrhage or high bleeding risk by NICE criteria
• neuraxial timing (start when safe)
• existing therapeutic anticoagulation
• defined contraindication (e.g. severe thrombocytopenia)
• palliative intent or informed refusal

Procedure-specific high bleeding risk in moderate general surgery — the category that fuels the one-per-cent debate — is uncommon. What trials count as extra bleed from LMWH is not the same as the operation being inherently catastrophic-bleed territory.

Default prophylaxis — not default paperwork

Presume pharmacological thromboprophylaxis indicated; withhold only for narrow, objective exceptions.

That is not a rejection of NICE. It is acute illness and reduced mobility logic applied directly. The impact weighting — fatal PE prevented versus major bleed caused — supports default even when rates look close.

What does not follow is that the mandatory VTE assessment form delivers this. England measured form completion, not correct prescribing, not administration, not post-discharge extension. Inter-hospital variation in appropriate prophylaxis ran from forty to one hundred per cent while assessment compliance sat near ninety-five per cent.

NICE published NG89 acknowledging the national risk assessment tool had not been validated for identifying who will develop VTE. The programme was industrialised nationally — CQUIN, contracts, dashboards — without operational efficacy data. Excellence is ward execution: protocol plus contemporaneous checking, not another tick-box.

Stop treating equal percentages as equal outcomes.
Treat every inpatient as at risk until proven otherwise.

Default pharmacological prophylaxis for acute inpatients — unless a narrow withhold applies — is rational harm reduction. The VTE form was meant to help; it was never validated to prove it does. National policy counted the form. Patients needed the prescription.

Sources: Cochrane heparin prophylaxis in medical patients; Kotaska, Thrombosis Journal 2018; BMJ 2022 network meta-analysis non-cardiac surgery; AHRQ VTE prevention guide; Thrombosis UK/GIRFT survey 2019–20; NICE NG89; Horner et al. NIHR HTA 2024.

VTE assessment form was never the solution - prescribe and administer

 

Quality improvement · NHS · Venous thromboembolism

England measures VTE form completion. It does not measure whether patients received thromboprophylaxis.

Every year, millions of adults are admitted to NHS acute hospitals. Venous thromboembolism — deep vein thrombosis and pulmonary embolism — remains one of the commonest causes of preventable harm in that setting. The clinical answer has been clear for decades: identify who is at risk, and give pharmacological thromboprophylaxis when the bleeding risk allows. Low molecular weight heparin and related agents work. The point of admission is to stop clots, not to complete paperwork.

Yet what England industrialised after 2010 was not prophylaxis. It was the VTE risk assessment form.

What the form was supposed to do

The national VTE prevention programme required documented risk assessment on admission, aligned with NICE guidance. Trusts adopted the NHS VTE risk assessment tool. Boxes were ticked for reduced mobility, acute illness, age, obesity, active cancer, surgery, and other factors. Bleeding risk was weighed. A score or summary judgment followed: offer mechanical measures, offer pharmacological prophylaxis, or neither.

On paper, this is rational pathway design. In practice, the form became the product. CQUIN payments, standard-contract clauses, and board dashboards converged on one question: was the assessment done? National returns report that roughly nine in ten adult admissions now receive a documented VTE risk assessment. The operational standard is 95%. Compliance charts look like success.

But compliance with assessment is not compliance with prophylaxis. The programme's stated aim was DVT and PE prevention. The mainstay of that prevention, for most adult inpatients in acute hospitals, is chemical thromboprophylaxis. The form is one step on the way to a prescription. It is not the prescription. When the form becomes the national scoreboard, the pathway inverts: documentation is rewarded; delivery is assumed.

Structure without certainty

The VTE assessment form looks objective. It is structured, standardised, and mandated. That appearance is misleading.

Risk stratification through the form is still a clinical judgment wearing a template. Two doctors can admit the same frail, immobile, acutely unwell patient and complete the same form differently. One records high VTE risk and prescribes prophylaxis. Another records lower risk and does not. Inter-rater variation in VTE risk assessment is well described. Different validated risk assessment models applied to the same patients can recommend prophylaxis in as few as one in nine or as many as nine in ten. The Department of Health tool used across the NHS sits within that spectrum of classification behaviour.

The form also encodes a default of withholding treatment until risk is explicitly declared high enough. That is the opposite of how most acute admissions present. A patient occupying an inpatient bed in an acute trust is, by definition, there because ward-level care is required. They are immobile relative to normal life. They have an acute illness, a surgical insult, or an exacerbation of disease. NICE already lists acute illness and reduced mobility as indications to consider pharmacological prophylaxis. If the patient is in hospital, those criteria are usually already met before the first box is ticked.

The form therefore risks redundant work at best and active obstruction at worst. At best, it records what should already be obvious. At worst, it creates a false-negative pathway: a subjective "low risk" classification interrupts the route to prophylaxis, and the national system celebrates the completed assessment anyway.

Voluntary national audit data bear this out. The Thrombosis UK and GIRFT survey of 2019–20 found that among high-risk patients judged eligible for drug prophylaxis, appropriate prescribing aligned with NICE in about 88% of cases — but with enormous inter-hospital variation from 40% to 100%. Missed doses among patients who were prescribed prophylaxis occurred in roughly 8% of cases. A substantial share of hospital-associated VTE episodes were judged potentially preventable because of failures at multiple points in the pathway: missing or incorrect assessment, failure to reassess when the clinical picture changed, delayed or omitted prescription, wrong dose, or doses not given.

None of that is consistent with a reliable, objective filter standing between patients and effective prevention.

The missing national metric

Here is the striking gap. England knows, to the percentage point, how many admitted patients had a VTE risk assessment. It does not publish an equivalent national rate for pharmacological thromboprophylaxis prescribing across the whole admitted population.

That is not a technical limitation. Most acute trusts now run electronic prescribing and medicines administration systems. If a patient received enoxaparin, dalteparin, or fondaparinux for prophylaxis, that order is in the record. A national or regional audit could report:

• the proportion of adult inpatients prescribed pharmacological VTE prophylaxis within 14 hours of admission;
• the proportion in whom it was contraindicated or already anticoagulated;
• the proportion of prescribed doses actually administered.

These are straightforward queries on structured data. They would answer the question patients and clinicians actually care about: was prevention given? Instead, the system measures the proxy — the form — and treats it as if it were the outcome.

The absence of this metric is a policy choice, not a data problem.
When a national programme selects one easy-to-collect process measure and ignores the treatment that measure is meant to trigger, boards learn what gets measured. Trusts staff VTE coordinators to chase form completion. Pharmacy and ward teams — who actually prescribe and give heparin — are rarely held to the same national account. We have built a reporting architecture that cannot tell us whether the right patients received the right drug at the right time.

NICE quality standards call for prophylaxis within 14 hours when indicated. Local audit is encouraged. National industrialisation stopped at the assessment.

Inverting the logic

A different approach is to stop asking a variable questionnaire to rediscover what admission already implies.

At Scunthorpe General Hospital, general surgery adopted a departmental protocol: pharmacological thromboprophylaxis for all inpatients unless actively bleeding. That is not a rejection of NICE. It is NICE's acute-illness and immobility logic applied directly, with a narrow exception list instead of a subjective risk score. A quality improvement project led by foundation doctors then checked contemporaneously whether prophylaxis had been prescribed, gave feedback, and prescribed when admitting teams had not. The department already had a 90% rate of appropriate prescribing under the protocol. Reminding staff of guidelines alone changed nothing — the process was already embedded. Active ward-level checking and prescribing raised appropriate pharmacological prophylaxis to 95%, a statistically significant improvement.

The lesson is not that one small DGH is an outlier. The lesson is what had to be done to achieve high prescribing in a setting where assessment compliance was never the barrier. The barrier was execution at the bedside. A simplified rule — inpatient equals indication unless clearly excepted — plus frontline ownership produced rates at or above those seen in national audits of selected high-risk cases, on a broader denominator that included all general surgical inpatients, not a pre-filtered audit sample.

The principles are reproducible. Acute hospital inpatients outside mental health and purely community settings share a common feature: they are sick enough, and immobile enough, to justify considering drug prophylaxis unless an objective exception applies — active bleeding, existing therapeutic anticoagulation, a defined contraindication, palliative intent, or patient refusal. That exception list is shorter, clearer, and less variable than a risk assessment form interpreted differently by every admitting team.

General surgery was the proof of concept because the risk profile is concentrated. The same presumption extends logically across acute medical wards, where immobility and acute illness are the norm rather than the exception. What changes is not the principle but the exception list: medical inpatients carry more bleeding-risk complexity, and a mature protocol must capture that without reverting to a subjective score that lets patients fall through. The form should document why prophylaxis was not given, not gate whether it should be considered.

What should replace the form as the national object

The VTE assessment form may still have a place as a record of exceptions and contraindications, or as a prompt within electronic prescribing. It should not remain the primary national quality measure for VTE prevention.

If the intention is DVT and PE prevention, and chemical thromboprophylaxis is the mainstay, then the national object should be prescribing and administration, measured from electronic prescribing data:

1. Prescribed appropriately within 14 hours of admission, or exception documented.
2. Doses administered as prescribed, with omissions tracked.
3. Reassessment when clinical status changes — particularly before discharge in high-risk groups.

Risk assessment completion can remain in the background. It should not continue to stand in for a prevention pathway that many patients never fully receive because a subjective tick-box said they were low risk.

We spent fifteen years optimising a form.
It is time to measure what we meant to treat.

The epidemiology of hospital-associated thrombosis has not responded as one would expect if that form reliably delivered prophylaxis. The problem is not that prevention fails. It is that we built a structured, subjective gate where a simple presumption and a short exception list would better serve acutely ill, immobile inpatients — and we chose not to count the prescription.

Data sources: NHS England VTE Risk Assessment Collection (2025/26); Thrombosis UK / GIRFT National Thrombosis Survey (2019–20); NICE NG89 and QS201; Scunthorpe General Hospital ASGBI 2025 quality improvement abstract (SP5.12). 

 ©M HEMADRI 

Mandatory VTE assessment hit 95% compliance. National outcome data tell a different story.

Quality improvement · NHS · Venous thromboembolism

Mandatory VTE assessment hit 95% compliance. National outcome data tell a different story.

Scope of this post: This article is about the assessment-based process — how it was mandated, measured, and rewarded — and why national data suggest it did not deliver the guideline's stated aim. It is not an argument against thromboprophylaxis itself; that is a separate clinical question, covered in a follow-up post.

In June 2010, England launched one of the most ambitious patient-safety programmes in its recent history. Every adult admitted to an NHS hospital would receive a documented assessment of venous thromboembolism (VTE) risk. Thromboprophylaxis would follow for those who needed it. Trusts would report compliance quarterly. Financial penalties would bite if performance fell short. NICE had already published its guideline — CG92 in January 2010 — setting out what good prevention looked like. The aim was clear: reduce deep vein thrombosis (DVT), pulmonary embolism (PE), and the deaths that follow from hospital-associated thrombosis.

Fifteen years on, the compliance charts look like a quality-improvement textbook. National assessment rates climbed from roughly 53% in mid-2010 to above 90% within two years. From April 2013, when the target was raised to 95%, the NHS met it and kept meeting it — quarter after quarter, trust after trust. By 2019, the figure sat at 95–96% and barely moved. On paper, the programme worked.

But paper is the problem.

The wrong scoreboard

The NHS did not make thromboprophylaxis mandatory in the abstract. It made documented risk assessment mandatory — and then treated assessment completion as the primary measure of national success. CQUIN payments, standard-contract clauses, and board-level dashboards all converged on one question: was the form filled in?

That is a process metric — not whether the right patient received prophylaxis, whether doses were administered, or whether fewer patients developed clots. Root-cause analysis was part of the policy bundle, but compliance with assessment drove behaviour and reputation.

When a system optimises for what it measures, it should surprise no one when the measurement diverges from the outcome.

HES tells a different story

Hospital Episode Statistics (HES) do not record "hospital-acquired DVT" as a discrete field. What they do record — reliably, at national scale, year on year — is whether a DVT code appeared as a secondary diagnosis on an admission episode whose primary reason for hospital contact was something else. That is an imperfect proxy. It may include some pre-existing clots. It will miss silent events never coded. It cannot distinguish community DVT from thrombosis provoked by the index admission.

It is, nonetheless, the closest thing we have to a ten-year national signal of DVT arising in the context of hospital care — and that signal is not comforting.

Secondary DVT rate (England, HES)

Period	Per 100,000 episodes
2012/13	~166
2019/20	~210
2021/22	~225
2020/21 (COVID)	~253

Source: Hughes et al., BMJ Open 2025. SPC analysis shows significant upward trend from 2013 — when assessment compliance was already above 95%.

That is a red flag. It is proof that the assessment-based process the NHS built around the guideline — mandatory forms, compliance targets, central returns — did not produce the epidemiological pattern you would expect if that process were reliably reducing hospital-context DVT at scale. The failure lies in what was industrialised, not in the existence of thromboprophylaxis as a clinical intervention.

Compliance up. Secondary DVT coding up.
Those two lines were never supposed to run together.

The death data make it worse

If the assessment process were reliably triggering effective prevention among the patients the programme was designed to protect, we should see that in hospital-linked VTE mortality — deaths in hospital or within 90 days of discharge among people with a recent admission, with VTE on the death certificate. That is NHS Outcomes Framework indicator 5.1 (I00675), the official national outcome measure aligned with NICE's hospital-associated thrombosis framing.

Here the official narrative and the epidemiology part company.

The published story (rate) 72.8 → 62 Fatal VTE per 100,000 admissions 2007/08 to 2019/20 (61.2 in 2023/24) ✓ Widely cited as success

The epidemiology (count) 8,106 → 9,087 Absolute hospital-linked VTE deaths 2007/08 to 2019/20 (+12% pre-COVID) ↑ Significant upward SPC trend from 2013

The rate fell because the denominator grew faster than the numerator — adult hospital admissions increased by roughly a third over the same period — not because England was clearly putting fewer people in the ground from hospital-associated thrombosis.

A metric that dilutes the truth

Why does a falling rate mislead so convincingly? Because NHS OF 5.1 spreads fatal events across a denominator far broader than the population where those deaths actually occur.

National linkage work by Catterick et al. (BMJ Open, 2024), using the same case definition as the outcomes-framework indicator, found that 86% of hospital-linked fatal VTE followed emergency inpatient admission. Planned inpatient and day-case pathways together accounted for only about 12% of deaths — yet they form a large share of all admitted activity.

The indicator dilutes high-mortality emergency pathways across millions of lower-risk admissions.
A rate can fall while the count of people dying does not — and even rises.

Day cases are included in both numerator and denominator of OF 5.1, so a day-case surge could artefactually lower the rate. HES data rule that out: day cases rose in number but held at about one-third of activity for over a decade. Fatal VTE stayed anchored in emergency inpatient care. The problem is a rate-based metric on a heterogeneous admission base, sold on the promise of fewer clots and fewer deaths.

Well meaning guideline failed in practice

NICE CG92 — later updated as NG89 — describes a pathway: identify risk, prescribe appropriate thromboprophylaxis for those who need it, consider post-discharge extension where indicated, investigate incidents, learn from harm. That is more than a tick-box.

What England actually mandated and measured was the first step — documented VTE risk assessment — and treated completion of that step as if it stood for the whole pathway. Form completion, central reporting, and a 95% compliance target became the national product. Thromboprophylaxis remained in the guideline text; it did not become the national scoreboard.

That substitution is why I regard the guideline as well meaning but failed in practice: not because prevention is futile, but because the assessment-based process given statutory force was the wrong proxy for it.

Process–outcome decoupling

Metric	What happened	Signal
VTE assessment compliance	Target met, sustained, celebrated	✓
HES secondary DVT	Upward trend through compliance era	↑
Fatal VTE (absolute deaths)	Flat to rising from 2013; SPC significant	↑
Fatal VTE (published rate)	Modest decline; cited as success	↘

We optimised documentation and called it prevention.

What should change

Assessment completion should be a gateway metric, not the finish line. Outcomes would be tracked in absolute terms and pathway-specific strata — emergency medical admissions first — with prophylaxis administration audited alongside forms. Secondary DVT in HES would be monitored as a sentinel, coding caveats acknowledged but not deployed to dismiss the signal.

The lesson generalises beyond thrombosis. When a guideline becomes mandatory NHS activity with financial teeth, ask which part of the pathway was actually enforced. If the answer is a single process step — here, risk assessment — you may get excellent compliance on that step and no superior clinical outcome on the harm the guideline was written to prevent.

Coming next: Thromboprophylaxis on its own terms — evidence, delivery, and outcomes. This post stops where the national programme stopped measuring: at the form.

The clinical intention was humane. The assessment-based architecture was not equal to it.

References

1. NICE. Venous thromboembolism in over 16s (NG89). nice.org.uk/guidance/ng89
2. NICE. VTE: reducing the risk for patients in hospital (CG92). nice.org.uk/guidance/cg92
3. Department of Health. Report of the Independent Expert Working Group on Prevention of VTE. 2007.
4. NHS England / NHS Digital. VTE risk assessment quarterly data and CQUIN specifications, 2010–2020.
5. Catterick MD, Hunt BJ. Impact of the national VTE risk assessment tool in secondary care in England. Blood Coagul Fibrinolysis. 2014;25(6):631–635.
6. Hughes F, et al. HES DVT/PE trends. BMJ Open. 2025. doi:10.1136/bmjopen-2024-090301
7. Catterick MD, et al. Who dies from VTE after hospitalisation in England? BMJ Open. 2024. doi:10.1136/bmjopen-2023-078898
8. NHS England Digital. NHS Outcomes Framework 5.1 (I00675). Feb 2025 release
9. Nuffield Trust. Blood clots following hospital care. nuffieldtrust.org.uk
10. NHS England Digital. Hospital Admitted Patient Care Activity (HES). digital.nhs.uk
11. Hunt BJ, et al. VTE prevention: UK experience. Res Pract Thromb Haemost. 2023. PMC9903667