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Blood Clots (cont.)

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:

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.

Medically Reviewed by a Doctor on 5/27/2014

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