What Measures Prevent Blood Clot Risk and How?

Summary: The risk of blood clots can be reduced through regular movement, avoiding smoking and individualised medical precautions. If sudden shortness of breath, chest pain or one-sided leg swelling develops, call 112 or attend an emergency department.

Addressing the risk of blood clots involves creating a mobility plan based on individual risk factors and, where necessary, having a doctor prescribe preventive treatment. The risk of deep vein thrombosis and pulmonary embolism is assessed by considering age, surgery, prolonged immobility, pregnancy, cancer, certain diseases and a history of thrombosis together.

Remaining in the same position for hours, being bedbound after surgery or having a leg immobilised in a cast can slow blood flow. Risk also changes with age: venous thromboembolism risk has been reported to approximately double with each decade after age 40 (PMID 12814980 — Risk factors for venous thromboembolism, 2003). Prevention therefore involves more than ‘walking more’: it includes deciding with a doctor when movement should begin and whether medication or mechanical measures are needed. Outcomes of any surgical or interventional procedure may vary between individuals.

What Is Blood Clot Risk, and When Is Clotting Dangerous?

Blood clot risk is the likelihood of unwanted clots forming inside blood vessels and obstructing circulation. Clotting is a natural defence that stops bleeding after injury; however, it becomes dangerous when a clot forms in an intact vessel, grows or breaks away and reaches a vital organ such as the lungs.

In normal clotting, a plug seals the damaged part of a vessel and is broken down by the body in a controlled manner as healing progresses. Thrombosis is the partial or complete disruption of blood flow by a clot inside a vessel. Risk depends not only on clot size but also on the vessel involved, the extent of obstruction and whether the clot moves.

Blood clotting can have serious consequences particularly in the following situations:

• When a clot forms in a deep vein: Deep vein thrombosis, usually developing in the leg or pelvis, can impair circulation in the affected area.
• When a clot breaks away: A clot carried to the lungs through the circulation can cause pulmonary embolism.
• When a vital blood vessel is blocked: Sudden obstruction of circulation in the brain, heart or lungs requires emergency assessment.
• When it progresses unnoticed: Symptoms may be mild in some cases of venous thrombosis, so risk cannot be excluded based on pain severity alone.
• When new or rapidly changing symptoms occur: Sudden swelling of one leg, marked warmth or unexplained shortness of breath requires assessment for a clot.

3 main mechanisms contribute to clot formation: slowing of blood flow, damage to the inner vessel lining and increased tendency of the blood to clot. These can occur alone or together. Prolonged immobility, recent surgery, certain cancers, pregnancy and a personal history of thrombosis are considered during assessment (Risk factors for venous thromboembolism, PMID 12814980).

Clot risk and existing thrombosis are not the same. Having a risk factor does not mean a clot will necessarily form; equally, having no known obvious risk factor does not completely rule out thrombosis. Assessment considers symptoms alongside medical history, examination findings and imaging results when needed.

How Do Deep Vein Thrombosis and Pulmonary Embolism Develop?

Deep vein thrombosis (DVT) develops when blood flow slows and a clot forms in a deep vein, usually in the leg or pelvis. If part of the clot breaks away and travels through the veins and the right side of the heart to the lung vessels, pulmonary embolism occurs. These two conditions are linked stages of venous thromboembolism.

Thrombosis is generally explained by three mechanisms known as Virchow's triad:

• Slowing of blood flow: Prolonged immobility can reduce circulation through the deep veins.
• Damage to the inner vessel lining: Injury to the vessel wall can activate the blood clotting system.
• Increased tendency of the blood to clot: The balance between clot formation and breakdown may shift towards thrombosis.

Any of these three mechanisms can act alone, while several occurring together can also facilitate deep vein thrombosis. This model of development is discussed in Risk factors for venous thromboembolism (PMID 12814980).

Stage	Process occurring in the body
Clot formation in a deep vein	Blood cells and clotting components accumulate inside the vessel to form a thrombus.
Clot growth	The thrombus can enlarge where it formed and partially or completely obstruct venous blood flow.
Clot detachment	A detached fragment of the thrombus becomes an embolus carried by the circulation.
Reaching a pulmonary vessel	The embolus can block a pulmonary vessel, affecting lung circulation and the workload of the heart.

Not every deep vein thrombosis progresses to pulmonary embolism. However, the location and extent of the clot and individual clinical characteristics can change this likelihood. Pulmonary embolism can be serious not only because it reduces blood flow in the lungs, but also because it can cause a sudden pressure load on the right side of the heart.

Which Factors Increase Blood Clot Risk?

Factors that increase clot risk include prolonged immobility, major surgery, cancer, pregnancy, older age, obesity, smoking, previous thrombosis and certain inherited clotting disorders. Risk rises particularly when several factors are present at the same time; individual assessment considers temporary and persistent factors together.

Blood clotting is normally a protective process that stops bleeding. However, slow venous blood flow, vessel wall damage or an increased tendency to clot can create conditions for deep vein thrombosis. These three mechanisms are known in medicine as Virchow's triad.

Risk factors can be assessed in two groups according to how they change over time:

• Temporary factors: Major operations, fractures and trauma, casts or splints, hospitalisation, prolonged bed rest and a marked reduction in mobility.
• Individual factors: Older age, obesity, smoking, previous venous thrombosis or pulmonary embolism and a family history of thrombosis.
• Medical conditions: Active cancer, pregnancy and the postpartum period, certain heart diseases, severe infections and inherited or acquired disorders affecting blood clotting.
• Treatment-related factors: Certain oestrogen-containing medicines, some cancer treatments and long-term intravascular catheter use.

Smoking alone, for example, does not explain the entire risk. But when smoking, prolonged immobility and recent major surgery occur in the same person, conditions favouring clot formation may become more pronounced. Assessment therefore considers the combined factors rather than a single habit or disease.

Source: ‘Risk factors for venous thromboembolism’ (2003), PMID 12814980.

Outcomes of any surgical or interventional procedure may vary between individuals. Perioperative thrombosis risk and the need for preventive treatment are determined by considering procedure type, duration of restricted mobility, coexisting conditions and bleeding risk together.

What Can Be Done to Reduce Blood Clot Risk?

Reducing clot risk involves assessing personal risks, maintaining mobility, stopping smoking and controlling coexisting conditions. If deep vein thrombosis risk is high, the doctor considers measures such as preventive medication, compression stockings or intermittent pneumatic compression alongside the person's bleeding risk. The aim is to prevent unwanted thrombosis in vessels, rather than stop normal blood clotting.

Prevention plans differ between individuals. Previous venous thrombosis or pulmonary embolism, active cancer, pregnancy, older age, obesity, prolonged immobility and certain operations change the risk assessment. A body mass index of 30 kg/m² or above is considered the threshold for obesity and is considered alongside other factors. Venous thrombosis risk factors are assessed cumulatively, not in isolation (Risk factors for venous thromboembolism, 2003, PMID 12814980).

A preventive approach may include:

• Individual risk assessment: Tell the doctor about previous clots, thrombosis at a young age in the family, cancer treatment, pregnancy, hormone use and long journeys.
• Maintaining mobility: Avoid remaining in the same position for long periods; walk regularly and exercise the calf muscles as health allows.
• Stopping smoking: Smoking is a modifiable risk factor affecting vascular health. Hypertension, diabetes and weight management are also addressed as part of a comprehensive approach.
• Adequate fluid intake: Avoid dehydration unless a doctor has recommended fluid restriction. However, drinking water alone is not a treatment that prevents venous thrombosis.
• Medication review: Discuss hormone-containing medicines and current treatments with the doctor; do not stop prescribed medicines on your own because of fear of clots.
• Individualised preventive treatment: Low-molecular-weight heparin or other anticoagulants may be considered when risk is high. The medicine, dose and duration are chosen with bleeding risk in mind.
• Mechanical methods: Compression stockings or intermittent pneumatic compression may be used in some people. Products should not be chosen arbitrarily without correct sizing and assessment of suitability.

Anticoagulants are not medicines to use indiscriminately to ‘dissolve’ an existing clot; they are medical treatments aimed at limiting new clot formation or clot growth. Aspirin is not an appropriate preventive option for every type of thrombosis either. Herbal products, olive oil or a particular food do not replace doctor-planned preventive treatment.

The choice of medication and mechanical methods to prevent venous thrombosis is based on joint assessment of clotting and bleeding risks (Deep Vein Thrombosis Prophylaxis: State of the Art, 2018, PMID 29573919; Perioperative Venous Thromboembolism Prophylaxis, 2020, PMID 33276846).

Outcomes of any surgical or interventional procedure may vary between individuals. Preventive treatment should not be started without assessing the person's conditions, medicines and bleeding risk.

How Are Blood Clots Prevented After Surgery and Prolonged Immobility?

Clot risk after surgery and prolonged immobility is reduced through individual risk assessment, safe early mobilisation, adequate fluid intake, mechanical protection and, when needed, clot-preventing medication. The plan to prevent deep vein thrombosis and pulmonary embolism depends on the type of surgery, duration of immobility, bleeding risk and coexisting conditions.

A prevention plan involves more than one measure. Major orthopaedic surgery, prolonged bed rest and immobilising a leg in a cast or brace can slow venous blood flow. Previous thrombosis, older age, cancer, obesity, smoking and certain hormone treatments are also considered. Two people undergoing the same operation may therefore receive different prevention plans.

Which Precautions Can Be Used After Surgery?

• Early and safe mobilisation: Getting up when permitted by the surgeon and physiotherapist, taking short walks and continuing ankle movements in bed support venous circulation. In suitable patients, mobilisation may begin on the day of surgery or within the first 24 hours; timing varies with the operation and the person's general condition.
• Intermittent pneumatic compression: Cuffs around the legs inflate and deflate at intervals to help venous blood move upwards. The healthcare team determines how long the device should be used.
• Compression stockings: These are not necessary for every patient. Correct sizing and assessment of skin and circulation are required; an unsuitable size or incorrect use can cause pressure and skin problems.
• Clot-preventing medicines: Anticoagulants, commonly called blood thinners, may be prescribed when thrombosis risk is judged greater than bleeding risk. The medicine, dose and duration are individualised; patients should not start, stop or change the dose on their own.
• Adequate fluid intake: If there is no heart or kidney condition requiring fluid restriction, taking the amount of fluid recommended by the healthcare team may be supportive.
• Regular changes of position: Turning, sitting up and making brief movements at permitted intervals reduce immobility compared with staying in one position for long periods.

Selecting mechanical methods and medicines for perioperative prevention requires joint assessment of venous thrombosis and bleeding risks (PMID 33276846 — Perioperative Venous Thromboembolism Prophylaxis (2020)). Mechanical methods may take priority in some people who cannot use medication; both approaches may be combined when risk is higher.

What Should Be Considered During Prolonged Immobility at Home?

Discharge does not mean clot risk has completely ended. If there is a cast, brace or movement restriction, the home plan should be written and easy to understand:

• Clarify how often you may get up during the day and how far you may walk.
• If weight-bearing is prohibited, learn which foot and leg exercises are permitted.
• Before discharge, ask about the prescribed anticoagulant's timing, dose and what to do if a dose is missed.
• Report unusual bleeding, falls or new one-sided leg swelling to the healthcare team.
• Do not plan journeys involving prolonged sitting without assessment by the doctor overseeing follow-up.

Simply elevating or massaging the leg during bed rest does not replace a clot prevention plan. In particular, a leg with new one-sided swelling and pain should not be massaged; the possibility of thrombosis requires medical assessment.

Outcomes of any surgical or interventional procedure may vary between individuals. The healthcare team plans the method and duration of clot prevention after assessing individual thrombosis and bleeding risks.

What Are the Symptoms of a Blood Clot, and When Is Emergency Care Needed?

Clot symptoms may include sudden swelling, pain, warmth and colour changes, particularly in one leg. If sudden shortness of breath, chest pain, faintness or coughing up blood occurs as well, pulmonary embolism may have developed. Do not wait or drive yourself; call 112.

Deep vein thrombosis most often occurs in the deep vessels of the leg. Findings differ between individuals; some clots may progress without obvious symptoms. New one-sided symptoms should be taken seriously, especially after surgery, prolonged immobility or cast application.

Symptoms of Deep Vein Thrombosis

The following findings require same-day medical assessment for deep vein thrombosis:

• New swelling in one leg
• Unexplained calf or thigh pain and tenderness
• Increased warmth in the affected area
• Redness, bluish discolouration or a marked change in skin colour
• A visibly different circumference between the two legs
• A feeling of tightness that worsens when walking or standing
• Superficial veins appearing more prominent than usual

These symptoms are not specific to thrombosis; muscle injury, infection and other vascular problems can cause a similar picture. Symptoms alone do not confirm the diagnosis. A doctor's assessment and appropriate imaging investigate whether a clot is present and which vein is affected.

Emergency Signs of Possible Pulmonary Embolism

A clot from the leg reaching the lung vessels is called pulmonary embolism. If any of the following symptoms occurs, call 112 or seek emergency medical help:

• Sudden or rapidly worsening shortness of breath
• Chest pain that becomes more pronounced when breathing in
• Fainting, confusion or severe dizziness
• Coughing up blood
• Unexplained rapid heartbeat
• Bluish lips, cold sweats or marked weakness

Symptom pattern	Action required
New swelling, pain, warmth or colour changes in one leg	Assessment at a healthcare facility on the same day
Sudden shortness of breath, chest pain, fainting or coughing up blood	Call 112 without delay
Shortness of breath developing alongside leg symptoms after surgery	Seek emergency help because of possible pulmonary embolism
Mild but progressively worsening one-sided symptoms	Notify the relevant doctor without delay

Mild symptoms do not mean a clot is small or harmless. Massaging the suspected area or taking blood thinners without medical advice is inappropriate. Clot treatment is planned according to clot location, extent, bleeding risk and coexisting conditions.

How Are Thrombosis Diagnosis and Treatment Planned?

Thrombosis is diagnosed by assessing symptoms, personal risks, examination findings and appropriate imaging together. Treatment is planned according to the vessel involved, clot extent, pulmonary embolism risk, bleeding likelihood and coexisting conditions. The aim is to prevent growth of the existing clot and formation of new clots.

Which Investigations Are Used for Diagnosis?

A single test is not sufficient for every patient. The possibility of deep vein thrombosis is assessed clinically, particularly with one-sided swelling, pain or colour changes.

• Clinical assessment: The doctor asks when symptoms began and about recent surgery, prolonged immobility, cancer, pregnancy, smoking and previous thrombosis.
• D-dimer test: Measures substances produced during clot breakdown. A raised result alone does not establish thrombosis; infection, pregnancy, older age and the postoperative period can also raise the level.
• Doppler ultrasound: A commonly used first imaging method when investigating deep vein thrombosis in the legs. Vessel compressibility and blood flow are examined.
• CT pulmonary angiography: May be used when symptoms such as sudden shortness of breath, chest pain or low oxygen suggest pulmonary embolism and clinical assessment supports its use.
• Additional investigations: Kidney and liver function, blood count and bleeding risk help plan treatment safely.

What Determines Treatment?

For most patients, treatment centres on medicines called anticoagulants, commonly known as ‘blood thinners’. Rather than directly dissolving the clot, these medicines aim to prevent the existing clot from growing and new clots from forming.

Planning takes the following criteria into account:

• Whether the clot is in a superficial vessel or the deep venous system
• Whether the clot is confined below the knee or extends into larger vessels
• The presence of pulmonary embolism or a serious risk of embolism
• Recent surgery, active bleeding or a tendency to bleed
• Special circumstances such as pregnancy, cancer, kidney or liver disease
• Whether thrombosis developed after a temporary trigger or without an obvious cause

For deep vein thrombosis associated with a temporary risk factor, anticoagulant treatment often lasts at least 3 months. Duration may be extended or adjusted after jointly assessing the cause, recurrence likelihood and bleeding risk. The need to individualise treatment and prevention is also discussed in DVT and pulmonary embolism: Part II. Treatment and prevention (PMID 15222649).

Clot-dissolving drugs or catheter-based interventions may be considered with extensive clot burden, impaired circulation or certain high-risk pulmonary embolisms. These options are not used in every case of thrombosis; potential benefit is weighed against the risk of serious bleeding.

Outcomes of any surgical or interventional procedure may vary between individuals. Treatment is planned after assessing personal risks and clinical findings.

People taking anticoagulants should not change the dose or stop treatment on their own. Unexpected bleeding, black stools, vomiting blood, a severe headache or symptoms after trauma require prompt medical assessment.

What Should You Consider in Daily Life to Reduce Blood Clot Risk?

To reduce clot risk in daily life, avoid prolonged immobility, move regularly, drink enough fluids, avoid smoking and maintain follow-up for coexisting conditions. Because deep vein thrombosis risk varies between individuals, a prevention plan should be based on a doctor's assessment, particularly for those with previous thrombosis.

Seemingly small daily habits can help maintain venous circulation:

• Avoid staying in one position for long periods: When working at a desk or travelling, getting up and walking briefly about every 1–2 hours is helpful. If standing is not possible, moving the ankles up and down activates the calf muscles.
• Move regularly: Activities suited to the person's health, such as walking, support venous circulation. Exercise type and intensity should be chosen with regard to age, joint disease, cardiovascular health and previous surgery.
• Do not neglect fluid intake: Avoid dehydration, particularly in hot weather and on long journeys. However, people with fluid restrictions due to heart or kidney disease should not increase intake on their own.
• Stop smoking: Smoking is a modifiable factor that harms vascular health and is considered in thrombosis risk assessment.
• Monitor weight and chronic conditions: The combination of obesity, hypertension and restricted mobility can change the risk profile. Continuing check-ups and prescribed treatment is important.
• Do not rely on tight clothing: Comfortable clothes can make movement easier, but clothing choice alone does not prevent blood clots or embolism.

How Should You Stay Active on Long Journeys?

On long plane, bus or car journeys, the main aim is to prevent the legs from remaining still for hours. Short walks along the aisle, getting out of the vehicle during breaks and repeated ankle movements while seated are possible precautions.

Keeping the feet on the floor rather than crossing the legs, and avoiding constant pressure behind the knees, may be preferable. People with previous deep vein thrombosis or pulmonary embolism, pregnant women, those receiving active cancer treatment or those who recently had surgery should discuss personal risks with a doctor before travelling. Medical reviews also emphasise considering venous thrombosis risk factors together (PMID 12814980 — Risk factors for venous thromboembolism, 2003).

Can You Use Medication or Compression Stockings Without Medical Advice?

Blood-thinning medicines and medical compression stockings are not equally suitable for everyone. The medicine and dose, and the stocking's compression class, depend on bleeding risk, vascular examination, coexisting conditions and thrombosis history. Do not take medicine prescribed for someone else or stop or change current treatment without medical advice.

Garlic, olive oil and herbal products do not replace medical treatment to prevent deep vein thrombosis. Products described as ‘natural’ can also affect blood clotting and interact with medicines. Daily precautions help reduce risk but do not guarantee that a clot will not form.

Frequently asked questions

What can be done to prevent blood clots?

To reduce clot risk, move regularly, avoid prolonged immobility and smoking, and maintain follow-up for existing conditions. In situations such as surgery, a cast, pregnancy, cancer or previous deep vein thrombosis, preventive treatment is planned according to individual risk assessment. Sudden swelling, pain and warmth in one leg require same-day medical assessment.

What prevents a clot from breaking away and travelling?

Blood-thinning treatment may be prescribed after medical assessment to reduce clot growth and embolism risk; mechanical preventive methods are also used in some patients. The appropriate approach depends on clot location, bleeding risk and coexisting conditions. Sudden shortness of breath, chest pain, fainting or coughing up blood may indicate pulmonary embolism, so call 112 or attend an emergency department.

What should be done when blood needs to clot?

For active bleeding, apply continuous direct pressure with a clean cloth; call 112 for heavy, deep or persistent bleeding. People taking blood thinners should not stop their medicine on their own or use products believed to increase clotting. Recurrent bleeding from the nose or gums, or blood in urine or stools, requires medical assessment.

Does olive oil prevent blood clots?

Olive oil does not dissolve an existing clot or replace treatment to prevent deep vein thrombosis or pulmonary embolism. It can be part of a balanced diet, but it is not appropriate to attribute protection to a single food. For people at high clot risk, prevention relies on movement, mechanical methods and medication prescribed by a doctor when needed.

How can clot risk be reduced on long journeys?

Getting up and walking at regular intervals, moving the ankles while seated and avoiding clothes that constrict the legs may help reduce clot risk on long journeys. Drink enough fluids and avoid smoking and excessive alcohol. People with previous venous thrombosis, recent surgery or other risk factors should discuss an individual prevention plan with a doctor before travelling.

Do smoking and hypertension increase clot risk?

Smoking can contribute to thrombosis risk by harming blood vessels; hypertension is also an important part of overall vascular disease risk. Risk is assessed alongside age, immobility, obesity, surgical history and other diseases. Stopping smoking and monitoring blood pressure regularly are key steps towards protecting vascular health.

Who needs blood-thinning medication?

Blood-thinning medicines may be needed by people diagnosed with venous thrombosis or embolism, or assessed as high risk because of surgery, prolonged immobility or certain conditions. A doctor chooses the medicine, dose and duration after weighing clotting and bleeding risks together. These medicines should not be started, stopped or adjusted without medical advice; this information does not replace medical diagnosis and treatment.