What Is Thrombosis?

  • Haajar DafiriBachelor of Science with Honours – BSc (Hons), Biochemistry, University of Wolverhampton, UK

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Thrombosis is when a blood clot forms within an artery (arterial thrombosis) or vein (venous thrombosis), thus restricting blood flow throughout the body. It can be deadly if it breaks apart and moves to organs such as the heart, brain, or lungs. 

Read on to learn about the main causes and risk factors of thrombosis, the signs, symptoms, and complications it causes depending on its location, as well as its diagnosis, prevention, treatment, and prognosis (outlook). 



Thrombosis is a serious, life-threatening condition that occurs when a blood clot (a thrombus) forms in a blood vessel (an artery or a vein) or one of the heart chambers. The blood clot can obstruct blood flow in blood vessels or break apart and move to other parts of the body.1

Importance of understanding thrombosis 

It is essential to understand thrombosis; how and why it occurs as well as what to do if it develops because limited blood flow to organs like the brain, heart, or lungs can quickly become a medical emergency and be fatal if left untreated.2

Types of thrombosis 

There are two types of thrombosis:

  1. Arterial thrombosis: This occurs when a blood clot forms within an artery, thus cutting off blood supply from the heart to the rest of the body. It is the most common cause of heart attacks and strokes
  2. Venous thrombosis: This occurs when a blood clot forms within a vein, thus preventing blood from flowing back to the heart from the body. It is the most common cause of a pulmonary embolism (blood clot in the lungs)


Thrombosis is mainly caused by:3

  • Damage to the inner (endothelial) lining of blood vessels
  • Hypercoagulability: This refers to an increased tendency in blood clot formation. Many factors cause this, examples of which will be shared in the ‘Risk Factors’ section below
  • Venous or arterial blood stasis: This refers to a decrease in the rate of blood flow within a vein or artery. It often occurs due to a lack of movement for extended periods

Risk factors 

Multiple factors are thought to increase the risk of developing thrombosis including:3

  • Age: Those over the age of 60 are thought to be more susceptible to thrombosis
  • Pregnancy: Pregnancy may increase hypercoagulability, and increased tendency to experience blood clots
  • High cholesterol
  • High blood pressure 
  • Lifestyle factors: These include excessive smoking of tobacco which may increase hypercoagulability and sitting down for prolonged periods. The latter may occur due to bed rest or long flights. It may cause blood stasis, in which the rate of blood flow slows down
  • Family history of blood clots
  • History of stroke or heart attacks
  • Certain medications: Birth control pills, particularly those that contain oestrogen may increase hypercoagulability when used for long periods
  • Certain treatments or surgeries

Signs and symptoms 

The signs and symptoms of thrombosis vary mainly depending on its location, but also its size, and the severity of the complications it causes.4

Thrombosis causes the following signs and symptoms in each of the following affected body parts: 


  • Chest pain
  • Difficulty breathing when active or at rest
  • Pain when breathing in

Brain or neck 

  • Weakness
  • Slurred or garbled speech
  • Droop and loss of muscle control on one side of the face
  • Confusion 
  • Agitation 
  • Changes in behaviour


  • Chest pain or discomfort (Angina)
  • Difficulty breathing 
  • Dizziness
  • Fainting


  • Intense stomach or abdominal pain (especially after eating)
  • Bloating
  • Nausea
  • Vomiting
  • Diarrhoea (with blood in some cases)
  • Fever 

Artery in the arm or leg

  • Pale skin in the affected area
  • Cool skin in the affected area
  • Weakness and loss of ability to move affected arm or leg (numbness)
  • Tingling (pins and needles) that can be painful
  • Blisters, wounds, or sores
  • Skin falling off
  • Necrosis (tissue death)

A vein in the arm or leg 

  • Red or dark skin in the affected area
  • Warm skin in the affected area
  • Pain around the affected area
  • Swelling 


A healthcare provider will diagnose a suspected patient with thrombosis by conducting a series of tests in the following order:4

  1. Physical examination and medical history 
  2. Imaging tests: Examples of the main imaging tests that may be used include:
    • Computed tomography (CT) scan uses a computer and X-rays to take detailed images of internal structures within the body including bones, muscles, organs, and blood vessels 
    • Magnetic resonance imaging (MRI) uses a large magnet, radio waves, and a computer to take detailed images of internal structures within the body
    • Ultrasound uses sound waves (no radiation) to create detailed images and videos of soft tissues within the body such as blood vessels
    • X-rays for blood vessels e.g. angiogram (for both arteries and veins) or venogram (for veins alone) 
  3. Blood tests: These help the healthcare provider confirm the diagnosis of thrombosis by assessing certain blood components (like platelets that form clots), clot-formation markers, and heart damage markers (like troponin protein which appears in the blood during a heart attack). Usually, these components and markers would be elevated if the patient had an active blood clot at the time of testing. Elevated levels of the protein troponin in the blood can be a sign that the patient experienced a recent heart attack or is at increased risk of developing a heart attack


If left untreated, thrombosis can lead to severe and deadly complications including:5

Prevention strategies 

To prevent thrombosis, it is worth considering implementing the following strategies:6

  • Maintaining a healthy weight 
  • Eating a healthy diet: Ideally, a Mediterranean-based ‘’heart-healthy’’ diet that is high in plant-based foods (e.g. fruit, vegetables, and whole grains), and healthy fats (e.g. olive oil), but low in meat, saturated fats (e.g. butter), sugar, and trans fats (e.g. cakes and biscuits) 
  • Engaging in regular exercise: Up to 150 minutes of moderate-intensity exercise a week is recommended to keep the heart healthy and weight stable 
  • Sitting less and moving more: This does not even have to be to exercise or walking; just simply taking short breaks to stretch regularly can be beneficial 
  • Avoiding and/or stopping tobacco use: /this includes all forms of tobacco e.g. smoking, vaping, and even smokeless tobacco 
  • Taking certain medications if you are at risk:
    • Blood pressure medications: High blood pressure can damage blood vessels and increase the tendency of blood clot formation 
    • Blood-thinning medications: These prevent blood clot formation 
    • Cholesterol-lowering medications or statins: These help lower cholesterol levels, which, when elevated, can cause plaques (fatty deposits) to form in the arteries. Plaques increase the risk of developing thrombosis

Treatment options 

Treatment for thrombosis varies depending on its severity, location, and the complications it causes. 

Patients with thrombosis may be offered the following treatments:7

  1. Blood-thinners: Blood-thinners have two main classes including:
    • Antiplatelet drugs
    • Anticoagulants 
  2. Thrombolytic therapy: Involves inserting certain drugs into an IV line or catheter to prevent blood clots 
  3. Thrombectomy: This is a type of surgery that involves removing blood clots from an artery and/or vein

Prognosis and long-term outlook 

The prognosis or outlook of thrombosis varies depending on:7

  • The location of the blood clot
  • The length of time that the patient takes to seek help: The longer the patient takes to seek treatment for thrombosis, the lower the chances of a good prognosis
  • The complications it causes 
  • Whether the blood clot has moved into the bloodstream: A clot in the bloodstream is far worse and more dangerous than a clot that stays in its primary location because it can move to other organs such as the lungs, heart, or brain and lead to death


Thrombosis is a serious condition where blood clots form in arteries or veins, potentially leading to life-threatening complications if left untreated. Arterial thrombosis, affecting arteries, and venous thrombosis, affecting veins, are the two main types. Causes include damage to blood vessel linings, hypercoagulability, and blood stasis.

Risk factors include age, pregnancy, high cholesterol, and immobility. Symptoms vary by location but may include chest pain, difficulty breathing, weakness, and swelling. Diagnosis involves physical exams, imaging tests, and blood tests.

Complications can include pulmonary embolism, stroke, and heart attack. Prevention strategies include maintaining a healthy lifestyle and taking certain medications. Treatment options include blood thinners, thrombolytic therapy, and thrombectomy. The prognosis depends on factors such as clot location, treatment timing, and complications. Early detection and treatment are crucial for a positive outcome.


  1. Ashorobi D, Ameer MA, Fernandez R. Thrombosis. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 [cited 2024 Mar 4]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK538430/
  2. Mackman N. Triggers, targets and treatments for thrombosis. Nature [Internet]. 2008 Feb [cited 2024 Apr 9];451(7181):914–8. Available from: https://www.nature.com/articles/nature06797
  3. Rosendaal FR. Causes of venous thrombosis. In: Van Beek EJR, Büller HR, Oudkerk M, editors. Deep Vein Thrombosis and Pulmonary Embolism [Internet]. 1st ed. Wiley; 2009 [cited 2024 Apr 9]. p. 1–26. Available from: https://onlinelibrary.wiley.com/doi/10.1002/9780470745007.ch1
  4. Esmon CT. Basic mechanisms and pathogenesis of venous thrombosis. Blood Reviews [Internet]. 2009 Sep 1 [cited 2024 Apr 9];23(5):225–9. Available from: https://www.sciencedirect.com/science/article/pii/S0268960X0900040X
  5. Previtali E, Bucciarelli P, Passamonti SM, Martinelli I. Risk factors for venous and arterial thrombosis. Blood Transfus [Internet]. 2011 Apr [cited 2024 Apr 9];9(2):120–38. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3096855
  6. Phillips DR, Conley PB, Sinha U, Andre P. Therapeutic approaches in arterial thrombosis. Journal of Thrombosis and Haemostasis [Internet]. 2005 Aug 1 [cited 2024 Apr 9];3(8):1577–89. Available from: https://www.sciencedirect.com/science/article/pii/S1538783622163154
  7. Davies MJ. Pathology of arterial thrombosis. British Medical Bulletin [Internet]. 1994 [cited 2024 Apr 9];50(4):789–802. Available from: https://academic.oup.com/bmb/article-lookup/doi/10.1093/oxfordjournals.bmb.a072926

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Haajar Dafiri

Bachelor of Science with Honours – BSc (Hons), Biochemistry, University of
Wolverhampton, UK

Haajar Dafiri is a recent First Class BSc (Hons) Biochemistry graduate from the University of Wolverhampton with over 4 years of academic writing experience.
She has professional experience working in both labs and hospitals such as LabMedExpert and the NHS, respectively. Due to her ‘’outstanding undergraduate’’ academic achievements, she was awarded both the Biosciences Project Prize and the Biochemical Society Undergraduate Recognition Award.

From a young age, whenever words and science were involved, Haajar eagerly followed. Haajar particularly enjoys diving deep into intricate research articles and interpreting, analysing and communicating the scientificfindings to the general public in an easy, fun and organised manner – hence, why she joined Klarity. She hopes her unique, creative and quirky writing style will ignite the love of science in many whilst putting a smile on their faces.

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