Know Thrombosis: Recognizing the Signs and Symptoms of Dangerous Blood Clots

October 9, 2018

You might be shocked to learn that one of the leading causes of preventable death is something many people have never heard of — and often don’t know they have. One in four people worldwide are dying from conditions caused by thrombosis, making it a leading global cause of death and disability. When a blood clot forms in an artery or vein, it can lead to heart attack, stroke, or a life-threatening clot in the lungs or leg, causing venous thromboembolism (VTE).

In fact, VTE-related events cause more deaths each year in the U.S. and Europe than breast cancer, AIDS and motor vehicle crashes — combined. Yet public awareness of the condition is extremely low: according to a 2018 survey of American office workers[1], only one in 10 said they are most concerned about blood clots and 62 percent do not know what VTE is. And even though hospitalization is a major risk factor for VTE, many hospitals around the world do not have mandatory protocols in place to help prevent thrombotic conditions.

That’s why the International Society on Thrombosis and Haemostasis (ISTH) is celebrating the fifth anniversary of a global movement called World Thrombosis Day on October 13 that increases awareness of this often-overlooked condition.

“Thrombosis is one of the leading causes of death worldwide — one in four people are dying from conditions caused by thrombosis — yet the seriousness of the issue is underappreciated. The ISTH founded World Thrombosis Day five years ago to increase awareness of this serious medical condition, and now we reach billions of people around the world each year,” said Dr. Gary Raskob, PhD, Chairman of the World Thrombosis Day Steering Committee.

Here’s what you need to know about thrombosis:

  • Thrombosis is the formation of potentially deadly blood clots in an artery (arterial thrombosis) or vein (venous thrombosis).
  • When a blood clot forms in the deep veins of the leg, it is known as deep vein thrombosis (DVT).
  • If a blood clot travels in the circulation and lodges in the lungs, it is known as a pulmonary embolism (PE).
  • Together, DVT and PE are known as venous thromboembolism (VTE), a dangerous and potentially deadly medical condition. DVT + PE = VTE.
  • A blood clot that forms as a result of atrial fibrillation (AFib) is an example of arterial thromboembolism. If that clot breaks free, it can travel in the circulation and lodge in an artery in the brain and cause a stroke.

World Thrombosis Day is dedicated to educating people about the risk factors, signs, and symptoms of thrombosis. Up to 60 percent of VTE cases occur during or within 90 days of hospitalization. Women should also be aware of their increased risk for thrombosis during pregnancy or if they take estrogen-containing medications (birth control pills or hormone replacement therapy). A family history of thrombosis or certain genetic factors can also increase a person’s risk of developing blood clots.

If you are at elevated thrombosis risk, it is especially important to know the signs and symptoms of the condition so you can seek medical attention as soon as possible. Symptoms of a DVT include pain or tenderness, swelling, redness, discoloration or warmth in your calf and/or thigh. People with PE often experience shortness of breath, rapid breathing, chest pain (which may be worse with deep breaths), rapid heart rate and light-headedness and/or passing out. If you experience any of these symptoms, seek medical attention immediately.

During hospital stays, which can elevate risk simply by reducing physical activity and blood flow, all patients and/or their caregivers should remember to advocate for thrombosis prevention measures. People who are undergoing surgery or cancer treatment should know they are at even higher risk. Download the VTE Risk Assessment Checklist from the World Thrombosis Day website to bring to the hospital and talk to your healthcare professional about assessing your risk.

“It’s very hard to be an advocate for yourself when you’re sick and in pain,” says Carole Chrvala, a professional epidemiologist who suffered VTE in 2016. “My advice is to ask as many questions as you possibly can. Bring somebody with you that you trust to ask questions on your behalf. Good medical care is a team effort and the patient is a key player on that team, with important self-knowledge and awareness that increases the likelihood that healthcare decisions are tailored to the individual patient.”

For more information about thrombosis, visit

(1) International Society on Thrombosis and Haemostasis (2018). American Office Workers and Thrombosis Awareness. Atomik Research.

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