Blood Clots: Recognising DVT and Pulmonary Embolism Early
Venous thromboembolism covers two linked conditions: a clot in a deep vein, usually in the leg, and a clot that has travelled to the lungs. Together they cause a large number of preventable deaths, and both have recognisable presentations.
Deep vein thrombosis
A clot in a deep vein, most often the calf or thigh.
Signs, usually in one leg:
- Swelling, often noticeably more than the other side
- Pain or cramping, typically in the calf, often a persistent ache rather than a sudden tear
- Warmth
- Redness or a bluish discolouration
- Tenderness along the vein
- Veins near the surface looking more prominent
The key feature is asymmetry. Both legs swelling together is more likely to be heart, kidney, liver or venous insufficiency. One leg, new and unexplained, is the pattern to act on.
Some DVTs produce minimal symptoms, and the first sign is a pulmonary embolism.
Pulmonary embolism
A clot that has broken off and lodged in the lung circulation.
Signs:
- Sudden breathlessness, often disproportionate to activity
- Sharp chest pain that is worse on breathing in
- Rapid heart rate
- Cough, sometimes with blood
- Light-headedness or fainting
- A sense of impending doom
- In large clots, collapse
This is a medical emergency. Call emergency services. Do not drive yourself.
PE is frequently misattributed to anxiety, a chest infection or a muscle strain, which is why sudden unexplained breathlessness in anyone with risk factors deserves a low threshold for assessment.
Who is at risk
Immobility. Hospital admission, surgery particularly orthopaedic and abdominal, a limb in a cast, long-haul travel, prolonged bed rest.
Surgery and trauma, with risk elevated for weeks afterwards.
Cancer, which substantially raises clotting risk.
Pregnancy and the postpartum period, with the highest risk in the weeks after delivery.
Oestrogen-containing contraceptives and hormone therapy. The absolute risk in a healthy young woman remains low, but it is higher than baseline, and higher again with smoking, obesity or a thrombophilia.
Obesity.
Age, with risk rising steadily.
Previous clot, among the strongest predictors.
Inherited thrombophilias such as factor V Leiden.
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Smoking. Dehydration. Chronic inflammatory conditions.
Diagnosis
Clinical probability is scored first, commonly with the Wells score.
D-dimer measures clot breakdown products. Its value is in ruling out: a normal D-dimer in someone assessed as low probability makes a clot very unlikely. It is a poor rule-in test, because it rises in infection, inflammation, pregnancy, cancer, after surgery and with age.
Compression ultrasound of the leg is the standard test for DVT.
CT pulmonary angiography is the standard test for PE. A ventilation-perfusion scan is used where contrast or radiation is a concern, including in pregnancy.
Treatment
Anticoagulation, often called blood thinning, which does not dissolve the existing clot but stops it growing and allows the body to break it down while preventing new clots.
Direct oral anticoagulants such as apixaban, rivaroxaban, edoxaban and dabigatran are first-line for most people. Fixed dosing, no routine monitoring, fewer interactions than warfarin.
Warfarin is still used in specific situations including mechanical heart valves and antiphospholipid syndrome, with regular INR monitoring.
Low molecular weight heparin injections are preferred in pregnancy and in many cancer-associated clots.
Duration depends on the cause. A clot provoked by a temporary factor such as surgery is typically treated for three months. An unprovoked clot, or one with ongoing risk factors, often warrants longer or indefinite treatment, weighed against bleeding risk.
While on anticoagulants
- Take them exactly as prescribed; missed doses matter more than with most medicines
- Tell every doctor and dentist before any procedure
- Carry an alert card
- Report unusual bleeding, black stools, blood in urine, severe headache, or any head injury
- Be cautious with NSAIDs, which add bleeding risk
- With warfarin, keep vitamin K intake from green vegetables consistent rather than avoiding them
- Check interactions before starting any new medicine or supplement, including herbal products
Long flights and travel
Risk rises with journeys over about four hours, and more with longer journeys and repeated flights in a short period.
- Walk the aisle every two to three hours
- Do calf exercises in the seat: raise heels and toes alternately
- Stay hydrated and limit alcohol
- Avoid sleeping pills that keep you immobile for hours
- Wear loose clothing
- Aisle seats make movement easier
Graduated compression stockings reduce risk and are reasonable for higher-risk travellers. Aspirin is not an effective substitute for anticoagulation and is not recommended for flight-related clot prevention. Anyone at high risk should discuss prophylactic anticoagulation before travelling.
After hospital or surgery
A large share of clots occur after discharge rather than in hospital. Ask before leaving whether you need prophylaxis at home, how long it should continue, and what signs to watch for. Early mobilisation is part of the treatment, not an optional extra.
The short version
One swollen, painful, warm calf is a DVT until proven otherwise. Sudden breathlessness with sharp chest pain is a pulmonary embolism until proven otherwise, and needs an ambulance rather than a wait-and-see. The highest-value prevention is movement, during travel and especially after surgery.