Deep vein thrombosis

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

DVT usually presents with unilateral swelling, pain or tenderness, but examination is neither sensitive nor specific. Cellulitis, ruptured Baker cyst, muscle injury, superficial venous thrombosis, lymphoedema and chronic venous disease are common mimics.

NICE deliberately couples time-limited testing with interim treatment. Before interim anticoagulation, take baseline FBC, renal and hepatic function, PT and APTT, but do not wait for results unless there is a clinical reason to withhold treatment; review results within 24 hours.

Duration depends on recurrence and bleeding risk. A major transient provoking factor supports stopping after 3 months when the course was uncomplicated; unprovoked DVT often favours extended treatment after shared review.

Key points

Use the 2-level DVT Wells score: 2 points or more means DVT likely; 1 point or less means DVT unlikely.
Likely DVT: obtain proximal leg-vein ultrasound within 4 hours if possible; if delayed, give interim therapeutic anticoagulation and scan within 24 hours.
Unlikely DVT: obtain D-dimer within 4 hours; if delayed, give interim therapeutic anticoagulation while awaiting the result.
A positive D-dimer is not diagnostic; it triggers ultrasound. Consider an age-adjusted threshold for people over 50.
If initial proximal ultrasound is negative but D-dimer positive, repeat proximal ultrasound in 6–8 days.
Confirmed proximal DVT usually needs at least 3 months of anticoagulation; review provoked versus unprovoked risk, bleeding and recurrence at 3 months.
NICE generally offers apixaban or rivaroxaban first, but active cancer, triple-positive antiphospholipid syndrome, pregnancy, extremes of weight and renal/hepatic impairment alter choice.
Do not order thrombophilia testing while continuing anticoagulation or after a clearly provoked event unless a specific NICE indication will change management.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Venous stasis

Major surgery, trauma, hospitalisation, paralysis or prolonged immobility reduces calf-pump flow. Blood pooling in deep venous valve pockets favours local coagulation and thrombus propagation.

Endothelial injury

Surgery, fracture, inflammation or an indwelling venous catheter can disrupt or activate the endothelium. The injured surface supports platelet adhesion and coagulation.

Acquired hypercoagulability

Active cancer, pregnancy, the postpartum period and oestrogen exposure shift haemostasis towards thrombosis. Persistent inflammatory illness may add further risk, especially alongside immobility.

Persistent or inherited susceptibility

Previous unprovoked venous thromboembolism, antiphospholipid syndrome or selected inherited thrombophilias increase recurrence tendency. Testing is useful only when its result would change management.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Virchow factors converge
Stasis, endothelial activation and hypercoagulability act alone or together. Their balance explains why a transient event may provoke thrombosis in one person but not another.
2
Deep venous thrombus forms
Thrombin generation deposits fibrin and traps red cells, often near venous valve pockets. The clot may extend from calf veins into proximal femoral or iliac segments.
3
Obstruction causes limb symptoms
Venous outflow obstruction and local inflammation raise distal hydrostatic pressure. Fluid enters the interstitium, producing unilateral swelling, pain, tenderness and collateral superficial vein distension.
4
Embolisation or organisation follows
Part of the thrombus may detach and travel to pulmonary arteries. Residual clot can instead organise and recanalise, leaving damaged valves and chronic venous hypertension.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Typical lower-limb DVT

Unilateral calf or whole-leg swelling, deep venous tenderness, pitting oedema, increased circumference and collateral superficial veins.

Proximal/iliofemoral DVT

Whole-leg swelling, marked pain, groin/buttock symptoms or venous distension; carries greater embolic and post-thrombotic burden.

PhlegmasiaRed flag

Massive painful swelling, cyanosis, sensory/motor change or threatened perfusion from extensive venous occlusion requires emergency vascular/haematology assessment.

Pulmonary embolism cluesRed flag

Dyspnoea, pleuritic pain, tachycardia, haemoptysis, syncope, hypoxia or shock require immediate PE assessment.

Provoking factors

Recent surgery/trauma, significant immobility, pregnancy/postpartum, oestrogen, active cancer or an indwelling line affect probability and duration decisions.

Mimics

Cellulitis, haematoma, ruptured popliteal cyst, muscle tear, superficial thrombosis and unilateral lymphoedema can reproduce pain and swelling.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Two-level DVT Wells scoreFirst step
Why
Set the NICE diagnostic pathway before testing.
Interpretation and limitations
At least 2 points: DVT likely. 1 point or less: DVT unlikely. Record each component, including minus 2 when an alternative diagnosis is at least as likely.
02
Quantitative D-dimer
Why
Rule out DVT in an appropriate low-probability pathway and determine repeat imaging after a negative scan.
Interpretation and limitations
A negative result in DVT-unlikely excludes DVT; a positive result needs ultrasound. Consider age-adjustment over age 50 according to assay/pathway.
03
Proximal leg-vein compression ultrasound
Why
Confirm or exclude proximal DVT.
Interpretation and limitations
Non-compressibility confirms thrombosis. Negative scan plus positive D-dimer requires repeat proximal ultrasound in 6–8 days.
04
FBC, U&E/eGFR, LFTs, PT and APTT
Why
Choose and safely dose anticoagulation and establish bleeding/organ-function baselines.
Interpretation and limitations
Take before interim therapy if possible but do not await results routinely; review within 24 hours and adjust/stop if necessary.
05
Pregnancy test and targeted cancer assessment
Why
Identify major treatment modifiers.
Interpretation and limitations
Use LMWH-based obstetric pathways in pregnancy. For unprovoked DVT, NICE recommends history, examination and baseline bloods—not routine extensive cancer imaging without symptoms/signs.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Cellulitis

Skin infection causes warmth, erythema, tenderness and sometimes fever or a portal of entry. DVT more often produces deep venous tenderness and swelling without a dominant cutaneous focus.

Ruptured popliteal cyst

A Baker cyst can release fluid into the calf, causing acute pain and swelling. Knee symptoms or posterior cystic fluid on imaging support this mimic.

Muscle tear or haematoma

A clear exertional injury, focal muscle tenderness, bruising or anticoagulant-associated bleeding favours soft-tissue damage. Ultrasound can identify a collection while assessing venous compressibility.

Superficial vein thrombosis

A palpable tender cord with local erythema follows a superficial vein rather than causing diffuse deep swelling. Proximity to the deep system determines whether further imaging is needed.

Lymphoedema or chronic venous disease

Longstanding swelling, skin thickening, gaiter pigmentation or established varices favour a chronic process. Abrupt asymmetry or deep pain still requires exclusion of superimposed DVT.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01likelyWells score at least 2First stepClinically suspected DVT with a likely 2-level Wells score.

1First: proximal leg-vein ultrasound with result within 4 hours if possible.
2Next: if ultrasound cannot be obtained within 4 hours, take D-dimer, give interim therapeutic anticoagulation and obtain ultrasound within 24 hours.
3Next: if scan is positive, continue treatment; if negative, use D-dimer to decide discharge versus repeat scan.
4EscalationEscalation: after a negative scan with a positive D-dimer, stop interim therapeutic anticoagulation unless it is treating another indication, and repeat proximal ultrasound in 6–8 days; give clear PE and deterioration safety-netting.

02unlikelyWells score 1 or lessClinically suspected DVT with an unlikely 2-level Wells score.

1First: quantitative D-dimer with result within 4 hours; consider an age-adjusted threshold over age 50.
2Next: if the result is delayed beyond 4 hours, give interim therapeutic anticoagulation while awaiting it.
3Next: negative D-dimer excludes DVT; positive D-dimer leads to proximal ultrasound within 4 hours if possible, otherwise interim therapy and scan within 24 hours.
4EscalationEscalation: pursue another diagnosis when DVT is excluded, while safety-netting for PE or worsening symptoms.

03confirmedConfirmed proximal DVTPositive proximal ultrasound or other objective confirmation.

1First: offer apixaban or rivaroxaban when suitable; otherwise choose LMWH followed by dabigatran/edoxaban or LMWH plus VKA according to NICE modifiers.
2Next: treat for at least 3 months and address provoking factors, mobilisation, analgesia and PE warnings.
3Next: at 3 months reassess provoked/unprovoked status, recurrence risk, bleeding, preference, renal/liver function and cancer status.
4EscalationEscalation: seek specialist advice for pregnancy, triple-positive APS, severe renal/hepatic impairment, active cancer, extremes of body weight, recurrence on therapy or phlegmasia.

04special groupsChoice modifiersA condition that makes routine DOAC treatment uncertain or unsuitable.

1First: pregnancy/breastfeeding—use an obstetric/haematology LMWH pathway, not a DOAC.
2Next: established triple-positive APS—offer LMWH or UFH concurrently with a vitamin K antagonist for at least 5 days or until INR is at least 2.0 in 2 consecutive readings, then continue VKA alone.
3Next: renal/hepatic impairment, active cancer or weight below 50 kg/above 120 kg—select and monitor therapy with specialist/product guidance.
4EscalationEscalation: major bleeding, recurrent VTE or suspected HIT needs immediate anticoagulation review and specialist management.

Key medicines and prescribing safety4 treatments · regimens, roles and cautions

First-line NICE option for confirmed proximal DVT/PE when suitable.

Apixaban

10 mg orally twice daily for 7 days, then 5 mg twice daily; if extended prevention is chosen after 6 months, 2.5 mg twice daily.

Check renal/hepatic function, interactions and bleeding; use caution with creatinine clearance 15–29 mL/min. Contraindicated in active significant bleeding and not used for pregnancy/breastfeeding.

First-line NICE option for confirmed proximal DVT/PE when suitable.

Rivaroxaban

15 mg orally twice daily with food for 21 days, then 20 mg once daily with food; after at least 6 months, 10 mg once daily (or 20 mg once daily if recurrence risk is high).

Check renal/hepatic function, interactions and bleeding. The 15 mg and 20 mg doses must be taken with food; contraindicated in pregnancy/breastfeeding.

Therapeutic LMWH for interim treatment and when LMWH is preferred, including pregnancy pathways.

Enoxaparin

1 mg/kg subcutaneously every 12 hours (or 1.5 mg/kg once daily in selected uncomplicated patients); if creatinine clearance is 15–30 mL/min, use 1 mg/kg once daily.

Dose by actual weight. Enoxaparin is not recommended when creatinine clearance is below 15 mL/min outside prevention of thrombus in the extracorporeal dialysis circuit. Monitor platelets/bleeding and consider anti-Xa in selected pregnancy, extremes of weight or renal impairment. Avoid with previous HIT.

NICE alternative after initial LMWH when apixaban/rivaroxaban are unsuitable.

Dabigatran

150 mg orally twice daily after at least 5 days of therapeutic parenteral anticoagulation. Use 110 mg twice daily at age 80 years or older or with concomitant verapamil; consider 110 mg twice daily at age 75–79, CrCl 30–50 mL/min, gastritis/oesophagitis/reflux or other increased bleeding risk.

The lower DVT/PE dose is based on pharmacokinetic/pharmacodynamic analyses rather than study in this clinical setting. Contraindicated if CrCl <30 mL/min; review P-glycoprotein interactions and bleeding. Capsules must be swallowed whole.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Pulmonary embolism

A detached thrombus can obstruct pulmonary arteries, causing pleuritic pain, dyspnoea, hypoxaemia, syncope or shock. Proximal DVT generally carries a higher risk of clinically important embolisation than isolated distal disease.

Post-thrombotic syndrome

Residual obstruction and valve damage create chronic venous hypertension. Persistent pain, heaviness, oedema, pigmentation and ulceration may substantially impair mobility and quality of life.

Phlegmasia and venous gangrene

Extensive iliofemoral occlusion can cause massive swelling, cyanosis and severely reduced microvascular perfusion. Sensory or motor change indicates threatened limb viability and demands emergency specialist assessment.

Recurrent venous thromboembolism

Persistent provoking factors, cancer, thrombophilia or an unprovoked first event can lead to recurrent DVT or PE. Recurrence risk influences the duration of anticoagulation.

Chronic thromboembolic pulmonary disease

Incompletely resolved or recurrent pulmonary emboli may organise within pulmonary arteries, causing persistent breathlessness, pulmonary hypertension and right-heart strain in a minority of patients.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Review baseline FBC, renal/liver function and coagulation results within 24 hours of starting interim treatment.
For DOACs, check adherence, bleeding, interacting medicines and renal/liver function at least annually and more often with frailty, CKD or intercurrent illness.
For LMWH, monitor weight-based dosing, platelets and renal function; use anti-Xa only in selected specialist contexts.
At 3 months, make and document the stop/continue decision using provoking factors, recurrence and bleeding risk plus patient preference.
Assess persistent swelling, pain, skin change and ulceration for post-thrombotic syndrome and reinforce urgent PE symptoms.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

The clock applies to D-dimer too

NICE uses a 4-hour target for both scan and D-dimer results; interim anticoagulation prevents untreated delay.

One negative scan may not finish the pathway

Negative proximal ultrasound plus positive D-dimer requires a repeat scan in 6–8 days.

Take bloods, then treat

Baseline tests should be drawn before interim anticoagulation when possible, but routine waiting for results defeats the pathway.

Provoked is a management label

Classify the provoking factor explicitly because it drives the 3-month review; minor or persistent factors may not carry the same low recurrence risk as major transient surgery.

Cancer search is targeted

For unprovoked DVT, do not add CT cancer screening without relevant symptoms or signs after history, examination and baseline tests.

11Common pitfallsFrequent interpretation and management errors.

01
Ordering D-dimer in a DVT-likely patient and delaying ultrasound rather than following the NICE sequence.
02
Stopping after one negative proximal scan despite a positive D-dimer.
03
Giving rivaroxaban 15 mg or 20 mg without food.
04
Using a DOAC in pregnancy or established triple-positive APS without specialist justification.
05
Calling a DVT unprovoked without documenting recent surgery, immobility, oestrogen, pregnancy and cancer context.