In a deep vein thrombosis (DVT), a blood clot (thrombus) forms in a deep vein — usually in the leg veins, less often in arm, pelvic or abdominal veins. The clot can obstruct blood flow and cause symptoms.¹
The greatest danger of a thrombosis is a pulmonary embolism: if part of the clot breaks off and travels through the bloodstream into the lungs, it can block pulmonary vessels there. A pulmonary embolism can be life-threatening.¹,²
Thrombosis and pulmonary embolism are together referred to as venous thromboembolism (VTE).
2. What is a pulmonary embolism?
In a pulmonary embolism (PE), a blood clot — usually from a deep leg vein thrombosis — blocks one or more vessels in the lungs. Depending on the size of the clot, a pulmonary embolism can range from mild (few symptoms) to life-threatening (circulatory failure).¹
Emergency: suspected pulmonary embolism
With sudden shortness of breath, chest pain or palpitations — especially if one leg is swollen at the same time — call the 112 emergency number immediately (in the US: 911).
3. Symptoms
Deep vein thrombosis (leg)
One-sided swelling of the leg — the key symptom; the lower leg or the whole leg
Pain — often in the calf area, worse with exertion or pressure
A feeling of warmth and redness or a bluish discolouration
A feeling of tension, a feeling of heaviness
Shiny, taut skin
Pulmonary embolism
Sudden shortness of breath — the most common symptom
Breathing-dependent chest pain (a stitch when breathing in)
In a severe pulmonary embolism: circulatory instability, dizziness, loss of consciousness
Symptoms can be non-specific
The symptoms of a pulmonary embolism are not always clear-cut. If it is suspected, always seek medical help — better once too often than too rarely.
4. Risk factors
Virchow's triad describes the three main factors that promote a thrombosis: slowed blood flow, vessel wall damage and an increased tendency to clot.¹
Acquired risk factors
Immobilization — prolonged bed rest, a cast, long flights or car journeys
Surgery — especially hip and knee surgery, abdominal surgery
Cancer — considerably increases the risk of thrombosis
Previous thrombosis or pulmonary embolism — markedly increased risk of recurrence
Varicose veins (varicosis) — disputed as an independent risk factor, but frequently associated
Genetic risk factors (thrombophilia)
Factor V Leiden mutation — the most common genetic clotting disorder
Prothrombin mutation
Protein C, protein S or antithrombin deficiency
Thrombophilia testing not routine
A genetic evaluation is usually not recommended routinely, only in certain constellations (e.g. thrombosis at a young age, familial clustering, recurrent thromboses).¹
5. Diagnosis
Deep vein thrombosis
Clinical probability: the Wells score helps to estimate the likelihood of a DVT and to determine the further diagnostic approach.
D-dimers: a blood test. Elevated D-dimers can point to a thrombosis but are non-specific (also raised with infections, after surgery, in older age). Normal D-dimers with a low clinical probability usually rule out a thrombosis.
Compression ultrasound: ultrasound of the leg veins — the standard method. Fast, painless, without radiation.
Pulmonary embolism
CT angiography (CTPA): the imaging of choice when a pulmonary embolism is suspected. Shows the clots in the pulmonary vessels directly.
Echocardiography: in unstable patients it can give signs of right heart strain and support the diagnosis.
Laboratory: D-dimers, troponin, BNP/NT-proBNP for risk assessment.
Treatment of VTE usually consists of anticoagulation (blood thinning), which stops the clot from growing and gives the body time to break it down.¹
First lineDOACs (direct oral anticoagulants)
In the current guideline they are recommended as first-line therapy for most patients.¹
Rivaroxaban, apixaban, edoxaban, dabigatran
Advantages: a fixed dose, no regular blood tests (INR), fewer food interactions than vitamin K antagonists. The individual agents differ in how often they are taken and in their indications.
EstablishedVitamin K antagonists
Phenprocoumon (Marcumar), warfarin
Long established. They require regular INR checks and a controlled vitamin K intake. They are preferred in certain constellations (e.g. antiphospholipid syndrome, a mechanical heart valve).
SpecificLow-molecular-weight heparin (LMWH)
Enoxaparin, tinzaparin and others
Usually used in the initial phase (as a bridge) or in cancer patients. An injection under the skin.
AdjuvantCompression therapy
Compression stockings
Can be used for leg swelling and to relieve symptoms. The role of compression in preventing a post-thrombotic syndrome is currently under debate.
In a severe pulmonary embolismThrombolysis (dissolving the clot with medication) or, in rare cases, surgical/interventional procedures. These measures are usually carried out in an intensive care unit.
The duration of anticoagulation depends on whether the thrombosis was triggered by a temporary risk factor or occurred unprovoked.¹
Provoked VTE
E.g. after surgery, immobilization, a cast — usually three to six months of anticoagulation. After that, the risk of recurrence is usually low.
Unprovoked VTE
No clearly identifiable trigger — the risk of recurrence is higher. Usually extended or even permanent anticoagulation is considered. The decision is made individually, weighing the risk of recurrence against the risk of bleeding.
Cancer-associated VTE
Anticoagulation usually for as long as the cancer is active or being treated.
Do not stop blood thinners on your own
Even with a stable finding, anticoagulants should never be paused or stopped on your own — the risk of recurrence is too high. Before operations, dental procedures or endoscopies, anticoagulation is always adjusted in consultation with the treating practice.
8. Prevention
Movement — avoid prolonged sitting and standing, move your legs regularly, on flights get up and circle your feet
Compression stockings — for longer flights or with an increased risk
Thrombosis prophylaxis in hospital — heparin injections after surgery and during bed rest (usually done as standard)
Take DOACs on time, keep an eye on the INR with Marcumar, check interactions with painkillers and antibiotics — the therapy stands and falls with adherence. Missed doses increase the risk of recurrence, too much increases the risk of bleeding. brite helps you keep the balance.
Medication reminder — apixaban twice a day, rivaroxaban once a day with a meal, Marcumar according to an individual dosing schedule, LMWH injections for the initial phase: brite reminds you on time. With DOACs, consistent timing is especially important — the half-life is short. Set up a reminder
Interaction check — blood thinners are highly interactive medications: NSAIDs (ibuprofen, diclofenac) increase the bleeding risk, some antibiotics (clarithromycin) and antifungals can raise DOAC levels critically, St. John's wort lowers the effect. brite shows the critical combinations right away. Check now
Health history — document INR values (with Marcumar), leg circumference, symptoms, signs of bleeding (nosebleeds, bruises, haematuria) and the duration of therapy. At your next appointment in angiology or cardiology, this is the basis for the decision to "extend or stop". Track your history
Digital medication plan — all your medications clearly laid out for your family doctor, angiology and cardiology. In emergencies or before operations, the crucial pointer: anyone taking blood thinners must be able to tell every provider immediately. Go to medication plan
FAQ: Common questions about thrombosis and pulmonary embolism
A thrombosis is a blood clot in a deep vein (usually the leg). A pulmonary embolism arises when part of this clot breaks off and is carried into the lungs. The pulmonary embolism is a complication of the thrombosis and can be life-threatening.¹
It depends on the cause of the thrombosis: for a provoked VTE (e.g. after surgery), usually three to six months. For an unprovoked VTE, extended or permanent anticoagulation is often considered. The decision is made individually.¹
Usually yes — exercise is in fact recommended. Sports with a high risk of injury (contact sports, martial arts) should usually be avoided, as blood thinners increase the bleeding risk. Discuss the level of activity with your treating practice.
Direct oral anticoagulants (e.g. rivaroxaban, apixaban) — blood thinners in tablet form that are recommended as first-line therapy for most patients. Advantages over Marcumar: a fixed dose, no regular INR checks, fewer food interactions.¹
Compression stockings can be helpful for leg swelling and to relieve symptoms. The routine recommendation for everyone affected is currently debated — newer studies suggest the benefit in preventing a post-thrombotic syndrome may be smaller than assumed. Discuss the decision individually with your practice.
Yes. The risk of recurrence depends on the cause: for provoked thromboses (e.g. after surgery) it is low. For unprovoked thromboses it is considerably higher. Extended anticoagulation can lower the risk of recurrence.¹
Yes — sitting for a long time with bent legs slows blood flow. Measures: get up regularly, circle your feet, drink enough, and wear compression stockings if your risk is increased.
Not routinely. A genetic evaluation is usually recommended only in certain constellations: thrombosis at a young age, familial clustering, recurrent thromboses. The decision is made by the treating practice.¹
Medical disclaimer: This article is for general information and does not replace medical advice, diagnosis or treatment. If a pulmonary embolism is suspected, call the 112 emergency number immediately (in the US: 911). Blood thinners should not be stopped, dosed or paused on your own. Treatment planning is always determined individually by the treating practice. Last updated: April 2026.
