Blood Clots

  • Medical Author:
    Benjamin Wedro, MD, FACEP, FAAEM

    Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

Quick GuideDVT in Pictures: Symptoms of Deep Vein Thrombosis, Beyond Leg Pain and More

DVT in Pictures: Symptoms of Deep Vein Thrombosis, Beyond Leg Pain and More

What are the signs and symptoms of blood clots?

Signs and symptoms of blood clots in the veins

Blood clots in the veins do not allow blood to return to the heart, and symptoms occur because of this "damming effect." These clots often occur in the legs or the arms, symptoms include:

  • swelling,
  • warmth,
  • redness, and
  • pain.

Most often, only one leg or arm is affected and the swelling occurs over the course of many hours. Because the leg or arm becomes red, warm and swollen, it is sometimes difficult to decide whether the cause is a DVT (deep vein thrombosis) or an infection.

On occasion, the whole leg may become very swollen, painful and turn bluish due to a blood clot located in the femoral vein in the upper leg or the iliac vein in the pelvis. This is called phlegmasia cerulia dolens. A similar situation may occur in the arm if the blood clot affects the subclavian vein located in the chest.

Signs and symptoms of blood clots in the arteries

Blood clots in the arteries do not allow blood to pump to an affected area. Body tissue that is deprived of blood and oxygen begins to die and becomes ischemic. Symptoms of blood clots in the arteries depend upon the location of the clot. Arterial blood clots cause diseases and illnesses that are medical emergencies, and it is appropriate to activate the emergency medical system or call 911.

Heart attack: Blood clots in the coronary arteries of the heart cause a heart attack. Symptoms of a heart attack may include:

The pain also may radiate to the arm, jaw or back.

Stroke or transient ischemic attack (TIA or "mini-stroke"): Blood clots to arteries in the brain may cause a stroke or transient ischemic attack (TIA). Symptoms may include:

FAST is the memory tool to remember regarding the symptoms for stroke:

  • Facial drooping
  • Arm weakness
  • Speech difficulties
  • Time (time is of the essence to try to reverse the stroke process. Call emergency services and get to a hospital.)

Blood clots that involve the mesenteric arteries that supply the intestine can cause significant abdominal pain, vomiting, and blood in the stool. This is called mesenteric ischemia.

What are the risk factors for forming blood clots?

The risk factors for arterial clots are those that are common to all diseases that cause narrowing of blood vessels, cholesterol plaque formation, and plaque rupture.

Blood clots in the veins are formed due to one of two main reasons: 1) immobility, and 2) genetic errors in the clotting mechanism. There are other associated risk factors including smoking and the use of birth control pills.

  1. Immobility: Commonly, when the body stops moving, the risk of blood clots increases since muscle movement is required to pump blood toward the heart. Stagnant blood in a vein is prone to clot. Examples of how blood clots may occur from immobility include:
  • Being hospitalized or bedridden after illness or surgery
  • Taking long trips (such as in a car, train, or plane), when hours may pass without standing to move, walk, or stretch, and blood pools in the leg veins and may potentially clot
  • Orthopedic injuries and/or has casts placed over broken bones or limbs
  • Undergoing knee or hip replacement
  • Pregnancy is a risk factor for forming blood clots in the legs and pelvis, due to insufficient blood flow back to the heart.
  • Immobility due to paralysis from a stroke or spinal cord injury.
  1. Genetic errors in the clotting mechanism: There may be a genetic or inborn error in the clotting mechanism, making a person hypercoagulable (hyper=more + coagulation= clotting) and at greater risk for forming clots.
Reviewed on 10/28/2016

Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest. 2012;141(2_suppl)

Dzsheka MS, et al. Stroke and bleeding risk in atrial fibrillation. Clin Cardiol.2014, Oct, 37(10)

Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.

Kearon, C., et al. "Antithrombotic Therapy for VTE Disease: Chest Guideline and Expert Panel Report." Chest. 2016;149(2):315-352. IMAGES:

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8.Brand X Pictures / Getty Images

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