Blood Clots

Blood clotting is a normal process that stops bleeding from injuries. But a clot forming inside an intact blood vessel — a thrombus — is dangerous. It can block blood flow and break off to lodge in the lungs, brain, or heart. Two particularly important conditions are deep vein thrombosis (DVT) — a clot in a deep leg vein — and pulmonary embolism (PE) — a DVT that has broken off and lodged in the lungs.

Deep vein thrombosis (DVT)

Symptoms:

• Swelling of one leg (less often both)
• Pain or tenderness — often in the calf or thigh, may feel like a cramp
• Warmth
• Redness or skin-tone changes
• Sometimes no symptoms at all
• See a doctor urgently — untreated DVT can become pulmonary embolism

Pulmonary embolism (PE)

A medical emergency — dial 112:

• Sudden breathlessness
• Sharp chest pain, worse with deep breathing
• Rapid heartbeat
• Coughing, sometimes with blood
• Sudden faintness, collapse, low blood pressure
• Anxiety, sweating

Risk factors

• Immobility — long flights, long car journeys, long hospital stays, bed rest
• Surgery, especially major orthopaedic, abdominal, or cancer surgery
• Pregnancy and the first few weeks after delivery
• Hormonal contraceptives, hormone replacement therapy
• Cancer
• Smoking
• Obesity
• Age
• Inherited clotting disorders (thrombophilia)
• Severe illness, infection (including COVID-19)
• Previous DVT or PE
• Central venous catheters

Diagnosis and treatment

• D-dimer blood test — usually the first step
• Doppler ultrasound of the leg — for DVT
• CT pulmonary angiogram — for suspected PE
• Anticoagulants (blood thinners) — the main treatment. Modern medicines allow many people to be treated at home.
• Severe PE — hospital care, sometimes clot-dissolving medicines or catheter-based interventions
• Treatment usually continues for at least 3-6 months; longer if the cause is permanent

Prevention

• Stay mobile — move around regularly on long journeys
• Stay hydrated
• Compression stockings for long flights if you're at higher risk
• For hospitalisation and major surgery — hospitals give preventive blood thinners and use compression devices
• Stop smoking
• Manage chronic conditions
• If you've had a clot before — follow your doctor's guidance for ongoing prevention
• Know the warning signs and act on them — early treatment prevents catastrophe