A deep vein thrombosis (DVT) is a condition in which a blood clot (thrombosis) forms within a deep vein and can be provoked or unprovoked [1]. 2.5-5% of the population will have a DVT in their lifetime [2].

Virchow’s triad explains the relationship between venous stasis, hypercoagulability and endothelial vessel wall in increasing the risk of thrombosis [2].

Risk factors include [1, 2, 6]:
  • Previous VTE (PE or DVT)
  • Cancer
  • Over 60
  • Immobilisation or paralysis
  • Recent surgery
  • Trauma
  • Prolonged travel over 4 hours
  • Smoking
  • BMI >30
  • Male
  • Pregnancy and peri-partum period
  • Varicose veins
  • Combined oral contraceptive or hormone replacement therapy
  • Dehydration
  • Nephrotic syndrome
  • Thrombophilia
  • Heart failure
  • Varicose veins
  • Antiphospholipid syndrome
DVTs most commonly affect the lower limbs, but can affect the upper limbs, with symptoms arising from the partial or complete obstruction of venous return. Signs and symptoms to assess for include:
  • Swelling and pitting oedema
  • Pain
  • Tenderness
  • Erythema
  • Warmth
  • Collateral vein distention
  • Symptoms of a PE – breathlessness, chest pain, collapse
  • Beware that cellulitis may look like or mask an underlying DVT
Differentials include [2, 6]:
  • Cellulitis
  • Muscle cramp
  • Muscle injury
  • Lymphoedema
  • Arterial insufficiency and peripheral arterial disease
  • Superficial thrombophlebitis
  • Compartment syndrome
  • Peripheral oedema 
  • Trauma
Assessment of Suspected DVT

Wells Criteria for DVT [3]
Active Cancer +1
Bedridden >3days or major surgery within 12 weeks +1
Calf swelling >3cm compared to the other leg (measured 10cm below tibial tuberosity) +1
Collateral veins +1
Localised tenderness along the deep venous system +1
Pitting oedema to the affected leg +1
Paralysis, paresis or recent plaster immobilisation +1
Previous documented DVT +1
Alternative diagnosis as likely or more likely -2

A flow chart of the NICE guidelines is included below, which uses the Wells Criteria in conjunction with a d-dimer. A d-dimer is a great "rule out" test but a poor "rule in" test (i.e. great sensitivity/negative predictive value but poor specificity/positive predictive value). This is because many things can cause a raised d-dimer, not just a DVT, e.g. inflammation, infection or pregnancy.

Figure 1: Assessment and investigation of suspected DVT from NICE guidance

Wells Score ≤ 1
A negative d-dimer is sufficient to rule out a DVT. However, if positive than an ultrasound scan can be used to confirm or rule out a DVT. If ultrasound cannot be obtained within 4 hours, anticoagulate the patient if no contraindications exist whilst awaiting an ultrasound scan.

Wells Score ≥ 2
Proceed to an ultrasound scan to confirm a DVT. If ultrasound cannot be obtained within 4 hours, anticoagulate the patient if no contraindications exist whilst awaiting an ultrasound scan.

If negative, perform a d-dimer which if negative rules out a DVT. If positive, anticoagulation isn't necessary but a repeat ultrasound scan in 6-8 days is recommended.

Management
  • Ensure baseline bloods have been obtained including clotting, full blood count, renal function and liver function [4]
  • Anticoagulation with treatment dose low molecular weight heparin, direct oral anticoagulants (DOACs) or warfarin (vitamin K antagonist (VKA)) [4]
  • Length of treatment is dependent if the DVT is provoked or unprovoked. If provoked treatment is for 3 months (or until reversal or the provoking factor), if unprovoked then longer treatment is considered [5]
  • Make sure to consider contraindications to anticoagulation!
  • If anticoagulation is contraindicated, a mechanical intervention can be considered such as vena cava filters
  • If an unprovoked DVT – investigation for undiagnosed malignancy or thrombophilia should be performed

Anticoagulation used in the treatment of DVT from NICE guidance

None of: renal impairment, active cancer, antiphospholipid syndrome or haemodynamic instability
Offer apixaban or rivaroxaban If neither suitable, offer one of:
  • LMWH for at least 5 days followed by dabigatran or edoxaban
  • LMWH and a VKA (e.g. warfarin)
    • Both are used together until 5 days or until the INR is ≥2.0 on 2 occasions, then the VKA is used alone
Renal impairment
Use the Cockcroft & Gault formula for estimated creatine clearance. 

If CrCl 15 to 50 ml/min 
  • Either the anticoagulation as above (bearing in mind that Dabigatran requires a CrCl ≥ 30 ml/min)
  • Alternatively UFH and a VKA
    • Both are used together until 5 days or until the INR is ≥2.0 on 2 occasions, then the VKA is used alone
If CrCl < 15 ml/min, offer one of: 
  • LMWH 
  • UFH 
  • LMWH or UFH and a VKA
    • Both are used together until 5 days or until the INR is ≥2.0 on 2 occasions, then the VKA is used alone
Note cautions and requirements for dose adjustments and monitoring in SPCs. Follow local protocols, or specialist or MDT advice

Active cancer
Those receiving antimitotic treatment, diagnosed in past 6 months, recurrent, metastatic or inoperable

Consider a DOAC If a DOAC is not suitable, consider one of:
  • LMWH
  • LMWH and a VKA
    • Both are used together until 5 days or until the INR is ≥2.0 on 2 occasions, then the VKA is used alone
Offer anticoagulation for 3 to 6 months Take into account the tumour site, drug interactions including cancer drugs, and bleeding risk

Antiphospholipid syndrome (triple positive, established diagnosis)
  • Offer LMWH and a VKA
    • Both are used together until 5 days or until the INR is ≥2.0 on 2 occasions, then the VKA is used alone
Complications [1]
  • Pulmonary embolus – always assess patient with suspected DVT for signs and symptoms of a PE.
  • Post-thrombotic syndrome (damaged deep veins results in pain, swelling, hyperpigmentation, ulcers or gangrene)
  • Recurrent VTE
Useful Resources and References
1. National Institute for Health and Clinical Excellence. Clinical Knowledge Summary: Deep Vein Thrombosis. (March 2020).
2. Royal College of Emergency Medicine. RCEM Learning Deep Vein Thrombosis (October 2017).
3. Wells P, Owen C, Doucette S et al. Does this patient have a deep vein thrombosis? JAMA 2006; 295: 199-207.
4. National Institute for Health and Clinical Excellence. NG158 – Venous thromboembolic disease: Diagnosis, management and thrombophilia testing. (March 2020).
5. Oxford University Hospitals. Outpatient DVT Service Protocols. (April 2019).
6. Patient. Deep Venous Thrombosis. (May 2020)

Written by Dr Hayley Boal (Clinical Fellow in Medical Education and Simulation)