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Medical Author:

Benjamin Wedro, MD, FACEP, FAAEM

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.

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Medical Editor:

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.

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In this Article

• Blood clot facts
• What are blood clots?
• What causes blood clots?
• What does a blood clot look like?
• What are the risk factors for blood clots?
• What types and conditions are caused by blood clots?
• What are the symptoms of blood clots?
• How are blood clots diagnosed?
• What is the treatment for blood clots?
• What are the complications of blood clots?
• How can blood clots be prevented?
• Patient Comments: Blood Clots - Describe Your Experience
• Patient Comments: Blood Clots - Causes
• Patient Comments: Blood Clots - Symptoms
• Blood Clots Index

Blood clots may cause life-threatening medical conditions, and are always considered in the differential diagnosis of any symptoms or signs. Differential diagnosis is the list of potential causes of a patient's condition, that is considered by the health care practitioner when caring for a patient.

Deep venous thrombosis and pulmonary embolism

Deep venous thrombosis may lead to a pulmonary embolism. If there is a blood clot or thrombus in a deep vein, it has the potential to break off (embolize) and flow through the veins back through the heart, and into the lung where it can become lodged in a small blood vessel, which prevents the lung from functioning. Pulmonary embolism is a medical emergency and can cause serious illness or death.

An embolus is the medical term for a blood clot that has moved with the bloodstream to a different location. With pulmonary embolus (pulmonary embolism), two issues occur.

1. The lungs' blood supply is comprised and the affected area of lung tissue may infarct, or die.
   
   
2. Because of the blockage, the ability of the lung to provide oxygen to the body is decreased and hypoxia (decreased levels of oxygen in the blood and throughout the body) may occur.

Even if venous blood clots do not embolize, they may cause significant local problems with swelling and pain. Since blood cannot return to the heart if a vein is blocked by a clot, the limbs may chronically swell and have decreased function in a condition called chronic thrombophlebitis.

Arterial thrombus

An arterial thrombus stops the blood supply to the tissues beyond the blockage, depriving cells of oxygen and nutrients. This quickly leads to tissue death. Arterial thrombus is the mechanism that causes:

• heart attack (when it occurs in the coronary arteries that supply blood to the heart)
  
  
• stroke (when it occurs in arteries within the brain), or
  
  
• peripheral vascular disease (occurring in the arteries of the legs).

Atrial fibrillation

In atrial fibrillation, small clots may form along the walls of the atrium or the upper chambers of the heart. Should one of these clots break off, it may embolize, or travel in the bloodstream to the brain, blocking an artery and causing a stroke. Other arteries may also be involved by this process, including those that supply the bowel. This can cause mesenteric ischemia (mesentery=lining of the bowel + ischemia=loss of blood supply) and potential necrosis (tissue death) of the intestine. Clots can also affect blood supply to fingers and toes.

Blood should clot anytime it becomes stagnant. This also means that clots will form when blood leaks out of blood vessels.

Examples include some of the following:

• With bleeding peptic ulcers, patients may vomit liquid blood mixed with clot.
  
  
• Patients with rectal bleeding may also have clot mixed with the bloody stool if there has been time for the clot to form.
  
  
• Sometimes patients with urinary tract or bladder infections develop associated bleeding in their urine, and small clots can form. On occasion these clots may be so big that they cannot be passed and block the urethra, preventing urination and causing urinary retention.
  
  
• Vaginal bleeding is a normal event for most women in the reproductive years and occasionally, blood can pool in the vagina and form clots before being expelled. If clots form in the uterus, they may cause significant pain and pressure as they pass through the cervix while being expelled.