Blood Clots

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, Chief Medical Editor

Melissa Conrad Stöppler, MD, Chief Medical Editor

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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• Blood Clots Overview
• Blood Clots Causes
• Blood Clots Symptoms
• When to Seek Medical Care
• Exams and Tests
• Blood Clots Treatment
• Self-Care at Home
• Medical Treatment
• Medication
• Surgery
• Next Steps
• Follow-up
• Prevention
• Synonyms and Keywords
• Author and Editor
• Viewer Comments: Blood Clots - Describe Your Experience
• Viewer Comments: Blood Clots - Cause

Blood Clots Overview

Blood flows throughout the body in arteries and veins supplying cells with nutrients, which allows them to function and remove waste products from metabolism. When blood vessels are damaged or begin to leak, blood is able to clot to repair the damage and restore integrity to the circulatory system.

The clotting mechanism involves a cascade of numerous factors that ultimately form the clot where it is needed. Initially, when a blood vessel is injured, the lining of the vessel attracts platelets that form an initial plug in the vessel wall. These platelets then release chemicals that activate a series of clotting factors called the clotting cascade. Ultimately, fibrin is formed, the protein that crosslinks with itself to form a mesh that makes up the final blood clot.

Picture of blood clotting

Blood flows through the body in a continuous loop. Blood is pumped through the body by the heart, but that same blood returns back to the heart both by gravity and by muscles in the arms and legs contracting and squeezing, or milking, the blood back to the heart. If blood becomes stagnant, it may clot and cause potential life-threatening conditions.

The medical term for a blood clot is a thrombus (plural: thrombi). An embolus refers to the situation in which the clot breaks and travels in the bloodstream to another location.

There are four potential outcomes regarding a blood clot. It will either

1. grow,
   
   
2. dissolve,
   
   
3. embolize, or
   
   
4. recannulate (a situation in which capillary blood vessels proliferate within the clot to re-establish blood flow)

Blood Clot Causes

Blood is supposed to clot to help repair a blood vessel that is injured. Clots or thrombi become a problem when they form inappropriately. There are a variety of illnesses and risk factors that can lead to blood clot formation.

Blood clots in the heart

Atrial fibrillation describes a heart rhythm in which the upper chamber of the heart does not beat in a coordinated fashion. Instead of having a single electrical impulse that allows the atrium to contract, hundreds of electrical impulses are generated, and the atrium jiggles like a bowl of Jello. This causes small blood clots to form along the lining of the atrium. The potential exists that these clots may break off and embolize to cause diseases such as stroke or ischemic bowel (loss of blood supply to part of the intestine).

Blood clots in veins

Deep vein thrombosis is the term used to describe clots that form in the veins of the arms or legs. Risk factors include:

• prolonged immobility,
  
  
• pregnancy,
  
  
• inherited blood clotting disorders,
  
  
• smoking, and
  
  
• hormone therapy including birth control pills.

Immobility may include recent surgery or hospitalization. This is especially a concern when a leg is involved that is immobilized in a cast or splint. This minimizes muscle movement in the extremity and increases the risk of blood clot formation. Prolonged airplane and automobile trips similarly minimize movement. Blood tends to pool by gravity in the lowest parts of the body. Without standing and walking at regular intervals, blood clots may form.

Blood clots in arteries

Blood clots may form acutely in an artery that has been gradually narrowed by plaque in vessels affected by arteriosclerosis. If the plaque ruptures, it initiates the clotting cascade. The risk factors for arterial clot are those commonly associated with heart attack, peripheral vascular disease, and stroke.

These include:

• high blood pressure,
  
  
• high cholesterol levels,
  
  
• smoking,
  
  
• diabetes, and
  
  
• a family history of cardiovascular disease.

Blood clots in other areas

When blood leaves blood vessels, it tends to pool and clot. Passing blood clots in the urine, the vagina, or in the stool is very frightening and should not be ignored. There may be a significant problem or the bleeding may be easily explained. For example, bleeding is commonly seen in bladder infections.

Bleeding or blood clots in the urine should not be ignored and presumed to be "just a bladder infection." The bleeding may arise from a bladder tumor or irritation of the bladder lining from other reasons (for example, cancer radiation therapy), or it may originate in the kidneys. Sometimes, if there is enough bleeding, clots will form in the bladder and may pass in the urine. This is commonly seen in older male patients with enlarged prostate glands that cause difficulty with urination.

Blood in the stool or rectal bleeding is never normal and should always be investigated. While hemorrhoids or anal fissures may be the source, bleeding may also come from a variety of other illnesses including tumors, inflammatory bowel disease, infections, and diverticulitis. Again, if there is enough bleeding present, blood clots may form and be passed as part of a bowel movement.

Passing blood clots from the vagina happens almost routinely. If blood from the uterus pools in the vaginal area, blood clots of varying sizes may form. Bleeding in pregnancy is never normal and medical advice should always be accessed in this situation, either by telephone or in person.