Travel-Related Venous Thromboembolism

Clots form through three factors: sluggish blood flow, blood that clots more easily, and injury to the vessel wall. A long journey of about four hours or more contributes the first, since sitting still in a confined space slows venous return from the legs, and the risk is similar by air, coach, car or train. It rises with journey length and with additional risk factors, and a clot can appear during travel or up to several weeks afterwards.

The paradox is that athletes are not shielded from this and carry established added risks: frequent long-haul travel, and above all lower-limb injury, immobilisation in a cast, or recent surgery, each of which strongly raises clot risk. A previous VTE and oestrogen exposure, such as the combined oral contraceptive pill, add further risk in the individual athlete. A distinct sport-related pattern is effort thrombosis, or Paget-Schroetter syndrome, an upper-limb DVT caused by repetitive overhead activity in swimmers, throwers, rowers and weightlifters, where the vein is compressed at the top of the chest.

Deep vein thrombosis of the leg typically causes swelling, aching or cramping pain, warmth and sometimes redness, usually in one leg, though it can be silent. Pulmonary embolism presents with breathlessness that may come on suddenly, chest pain that is worse on breathing in, a cough that may bring up blood, and a fast heart rate, and in severe cases collapse. In a fit young athlete these features are easily dismissed, so any suspicious presentation after long travel or a period of immobilisation should prompt objective assessment rather than reassurance.

Diagnosis starts with a two-level clinical probability score, the Wells score, which sorts suspected cases into likely or unlikely. For a likely DVT, a proximal leg vein ultrasound is done first; for an unlikely DVT, a D-dimer blood test is done first and, if positive, followed by ultrasound. If that first scan is negative but the D-dimer was positive, the scan is repeated after six to eight days. For a likely PE, computed tomography (CT) pulmonary angiography is arranged immediately; for an unlikely PE, a D-dimer is checked first. Recent strenuous exercise can raise D-dimer, so it is read within this pathway rather than used to override it. When the indicated D-dimer or scan cannot be obtained within the recommended timeframe, interim anticoagulation with a direct oral anticoagulant is started while awaiting the result.

Confirmed proximal DVT or PE is treated with anticoagulation for at least three months. Current UK guidance makes a direct oral anticoagulant (DOAC), usually apixaban or rivaroxaban, the first choice for most people, with low molecular weight heparin (LMWH) or other options where a DOAC is unsuitable, such as severe kidney impairment, very high or low body weight, or triple-positive antiphospholipid syndrome. Whether to stop at three months or continue depends on whether the clot was provoked by a temporary factor, the risk of it recurring and the risk of bleeding, and a long flight is not automatically treated as a major provoking factor.

For sport, the key issue is that anticoagulation raises the risk of serious bleeding, so contact and collision sports and other high-injury activities are avoided while the athlete is anticoagulated. Early mobilisation and graded non-contact activity can begin once the athlete is clinically stable and symptoms allow, building back up in stages. Specialist haematology input helps in complex cases, though it is not needed for every straightforward clot. Suspected pulmonary embolism with breathlessness, collapse or an unstable circulation is a medical emergency needing immediate hospital assessment.

Most prevention is simple and mechanical, and applies to journeys of about four hours or more. The traveller should move regularly, walk when possible, do seated calf exercises by pumping the ankles, choose an aisle seat where practical, and avoid sitting with the legs crossed. Sleeping tablets are best avoided, since the resulting immobility adds to the risk. Good hydration is sensible general advice for comfort, though the evidence that dehydration itself causes travel clots is weak, so it does not replace movement.

For travellers at substantially increased risk, properly fitted below-knee graduated compression stockings reduce clot risk and leg swelling. Higher risk includes a previous VTE, recent surgery or lower-limb immobilisation, active cancer, pregnancy and the weeks afterwards, and significant clotting disorders. Routine drug prophylaxis is not advised, since the evidence for it is weak and direct oral anticoagulants have not been studied for this purpose, and only selected travellers at the highest risk might be considered for low molecular weight heparin after specialist assessment. Aspirin is not recommended for preventing travel-related clots. Anyone recently treated for VTE, or after recent lower-limb surgery, a cast or a hip or knee replacement, should seek specialist advice before long-haul travel rather than relying on general measures.

• •Current NICE guidance on venous thromboembolic diseases covers diagnosis, the two-level probability pathways, anticoagulation and the first-line use of direct oral anticoagulants.
• •The British Society for Haematology 2010 guideline on travel-related venous thrombosis, with its 2023 addendum, sets out risk and preventive measures for long journeys.
• •NHS guidance describes the recognition of deep vein thrombosis and pulmonary embolism and general prevention for travellers.
• •Evidence specific to athletes is limited, so management follows general VTE guidance applied to the individual and the sport.

• •Venous thromboembolism covers deep vein thrombosis and pulmonary embolism, and journeys of about four hours or more are a modest risk that rises with immobility and other factors.
• •The athlete's paradox is that fitness does not exempt an athlete, and because clots are not expected in the fit and young, the diagnosis is easily missed.
• •Deep vein thrombosis is usually a swollen, painful, one-sided leg; pulmonary embolism brings breathlessness, pleuritic chest pain, coughing blood or a fast heart rate, and any suspected pulmonary embolism needs urgent assessment.
• •Use the two-level Wells score: for a likely clot, image first; for an unlikely one, D-dimer first, repeating a negative leg scan after six to eight days if the D-dimer was positive.
• •A direct oral anticoagulant is first-line for at least three months, and contact or collision sport is avoided while anticoagulated, with a graded non-contact return.
• •Prevent clots on long journeys by moving, calf exercises and an aisle seat, with compression stockings for those at substantially increased risk; routine drug prophylaxis and aspirin are not recommended.