Blood Clots Fact Sheet

Find out what you need to know about blood clots.

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How to Prevent Blood Clots (2:30)

Anyone who’s made a long-haul flight has heard of deep-vein thrombosis or DVT, as it’s commonly known. Longer periods of sitting, driving and flying have put more people at risk for clots. Should you be worried? Find out where exactly these clots come from, who’s at risk and how you can prevent them from forming.

What Is a Blood Clot?

Blood is supposed to clot when blood vessels are damaged. In doing so, they prevent blood from leaking out in places where it shouldn’t be while the body repairs the vessel wall. In healthy individuals, clotting generally provides a beneficial service and keeps the clot out the way of blood flowing past inside the vessel. Unfortunately, certain conditions that damage blood vessels and increase inflammation in the body can trigger the clotting system unnecessarily, leading to formation of a clot that blocks blood flow.

There are two main types of concerning clots: DVT and pulmonary embolus (PE). The DVT is often a precursor to the PE. Here’s how it works. As blood gets stuck behind a blockage (like a folded knee), certain components of the blood build up. If they congregate in an area more prone to damage or inflammation, a clot might start to form, setting off a chain reaction that grows and grows, blocking the vessel. This type of clot is called a deep-vein thrombosis (DVT). If a piece of that clot happens to break free, it can travel through your blood stream and lodge in your lungs. This blocks blood flow and prevents your body from getting oxygen, which can be deadly. This is called a pulmonary embolism (PE).

Who’s at Risk?

The following conditions can put you at risk for clotting:

  • Vein injury caused by fractures, muscle injury or surgery.
  • Slowed blood flow with long periods of sitting (especially cross-legged), being confined to bed, being paralyzed or limited movement.
  • Increased estrogen caused by birth control pills or hormone replacement therapy.
  • Chronic illnesses including heart diseasediabetes, lung disease, cancer and inflammatory conditions like Crohn’s disease, ulcerative colitis, lupus or rheumatoid arthritis.
  • Age, with risk increasing over time.

What are the Symptoms?

The symptoms vary depending on the type of clot. For a DVT, you might experience pain, swelling, redness and tenderness in the area. If a PE has occurred, you’ll have trouble breathing, chest pain, a fast or irregular heart rate and low blood pressure that may cause you to faint.