Blood Clots

Medically Reviewed By William C. Lloyd III, MD, FACS

What are blood clots?

A blood clot is an organized clump of hardened blood. Normal blood clotting helps stop blood loss, such as when you get a minor cut or scrape. However, a blood clot that forms inside a blood vessel (artery or vein) or in the heart is called a thrombus and is a serious medical condition. Blood clots can form in the superficial veins just below your skin, or they can form in the deeper, large veins (deep vein thrombosis). Blood clots can also dislodge and move from their initial location to another. This is called an embolism.

Blood clots are more common in people who cannot move around easily because of advanced age, injury, surgery, or disease. People with certain blood clotting disorders that make their blood clot more easily have an increased risk of developing blood clots in the deep veins. In addition, certain cancers and estrogen-based medications can increase your risk for blood clots.

A blood clot is dangerous because it can block or reduce the flow of blood to the part of the body in which it formed. This blockage causes a lack of oxygen to the tissues (called ischemia) and eventually leads to permanent tissue damage.

Blood clots can also break apart from the blood vessel wall and travel to another location, such as the brain or lung, leading to catastrophic consequences. A blood clot that travels to the lung can lead to a pulmonary embolism, permanent lung damage, and even sudden death. A blood clot that travels to the brain can cause a stroke. A blood clot that forms within the arteries of the heart can cause a heart attack.

Your risk of developing blood clots can be minimized by making certain lifestyle changes and following your doctor’s treatment plan. In particular, regular exercise, smoking cessation, elevating your feet, and frequently changing your body position can help prevent blood clots from forming.

What symptoms might occur with blood clots?

Blood clots can form without any related symptoms. However, there are certain hallmark symptoms that may accompany a blood clot:

  • Localized warm spot on your arm or leg

  • Pain upon standing or putting all of your weight on one leg

  • Skin redness

  • Soreness in your arm or leg

  • Unexplained swelling in your arm or leg

Serious symptoms that might indicate a life-threatening condition:

Blood clots can quickly become a life-threatening condition that should be immediately evaluated in an emergency setting. Seek immediate medical care (call 911) if you, or someone you are with, have any of these life-threatening symptoms.

Symptoms that might indicate a blood clot in your lung (pulmonary embolism) include:

Symptoms that might indicate a blood clot in your brain (stroke) include:

  • Abnormal pupil size or reactivity to light
  • Droopy eyelid
  • Sudden difficulty speaking
  • Sudden inability to understand speech
  • Sudden loss of coordination
  • Sudden vision problems

Symptoms that might indicate a blood clot in your heart arteries (heart attack) include:

  • Chest pain moving to your shoulder, arm, face, jaw, teeth, or belly
  • Shortness of breath

What causes blood clots?

Blood clots can form in response to several factors, including a sedentary lifestyle and underlying medical conditions that make your blood clot differently or reduce the flow of blood through the circulatory system. Your family history and genetic factors may also put you at an increased risk for blood clots.

Underlying medical conditions that are associated with blood clots

Certain medical conditions and procedures that can increase your risk for developing blood clots include:

  • Antiphospholipid syndrome
  • Genetic factors that make your blood more likely to clot (Factor V Leiden mutation)
  • Heart failure (deterioration of the heart’s ability to pump blood)
  • Pelvis and leg bone fractures
  • Recent catheter placement for surgical procedure or drug delivery
  • Recent surgery

    Lifestyle and other factors that are associated with blood clots

    Lifestyle and related factors include:

    • Advanced age
    • Family history of blood clots
    • Long distance air travel
    • Prolonged bed rest
    • Sedentary lifestyle

      Medications that are associated with blood clots

      Some medications that are known to increase blood clotting (hypercoagulability) include:

      What are the potential complications of blood clots?

      Because the complications of untreated blood clots can be serious and life threatening, it is important to reduce your risk by altering your lifestyle and following your medical treatment plan. Blood clots that break loose and travel to other parts of the body can lead to serious complications, including:

      Was this helpful?
      1. About Heart Attacks. American Heart Association.
      2. What is pulmonary embolism? National Heart, Lung and Blood Institute, National Institutes of Health.
      3. Collins RD. Differential Diagnosis in Primary Care, 5th ed. Philadelphia: Lippincott, Williams & Williams, 2012.
      4. Domino FJ (Ed.) Five Minute Clinical Consult. Philadelphia: Lippincott Williams & Wilkins, 2013.
      Medical Reviewer: William C. Lloyd III, MD, FACS
      Last Review Date: 2021 Jan 11
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      THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.