Knowing the Warning Signs of a Blood Clot Can Save Your Life


Awareness is critical and yet less than 50 per cent of Canadians know about Thrombosis (or blood clots),  a condition that is the underlying cause of the top three cardiovascular killers: heart attack, stroke and venous thromboembolism (VTE).  Even more concerning is that only 1 in 5 Canadians are concerned about the impact of blood clots on their health.

This lack of knowledge is the impetus behind Thrombosis Canada’s C-L-O-T-S awareness campaign which helps people recognize if they are experiencing a blood clot in their lungs (a pulmonary embolism or PE) or in their legs (a deep vein thrombosis or DVT).

The C-L-O-T-S campaign is based on an acronym that highlights the most common and easy-to-understand warning signs for blood clots: 

  • Chest Pain – a blood clot in the lung can cause lung damage and inflammation, resulting in sharp chest pain when breathing.
  • Light-headedness – a blood clot in the lung causes dizziness, especially if larger or multiple clots block blood flow to the lung.
  • Out of breath – a blood clot in the lung can reduce the amount of oxygen circulating in the body and cause shortness of breath.
  • Tenderness in the leg – a blood clot in the leg causes tenderness or cramping in the calf or behind the knee, as well as redness and warmth.
  • Swelling in the leg – a blood clot in the leg blocks blood flow in the veins that drain blood from the leg back to the heart, causing the leg to swell.

“As medical professionals, we saw the need to provide tools to increase public understanding about thrombosis,” says Dr. Deborah Siegal, assistant professor in the division of hematology and thromboembolism at Hamilton’s McMaster University.  

VTE or vein blood clots, is a significant public health problem, affecting about 100,000 Canadians and causing 10,000 deaths each year.  Annually, VTE causes more deaths in Canada than breast cancer, HIV and motor vehicle accidents combined.

A recent #KNOWTHROMBOSIS Survey commissioned by Thrombosis Canada showed that among people 65 and older:

  • 83 per cent are aware of blood clots, yet 54 per cent are not very concerned about the medical condition;
  • 77 per cent say they wouldn’t know what a blood clot in the vein would feel like;
  • 84 per cent say they wouldn’t know what a blood clot in the lung would feel like;
  • Half of respondents don’t know that being 65+ could increase their risk of developing a blood clot.

“The good news is that seniors recognize the seriousness of blood clots – 90 per cent know that having a blood clot is a medical emergency and 92 per cent know it can cause death,” says Dr. Agnes Lee, professor, department of medicine and medical director, thrombosis program, UBC and Vancouver Coastal Health.  “The key is to focus on educating Canadians to know what to look for and recognize what a blood clot may feel like.” 

Sandra Buckberrough agrees.  Recognizing the symptoms of a blood clot likely saved her life.  

After developing a superficial blood clot in her arm in 2016, the 51-year-old mother of three woke up to find a red, swollen lump in the back of her calf several months later.  Knowing the signs of a blood clot, it concerned her enough to see her family doctor the same day. Ultrasound testing confirmed the lump to again be a superficial blood clot that would resolve itself.  

Days later, Buckberrough noticed the redness and swelling were worsening. Within hours, she watched the clot travel from her calf to her thigh. Although her earlier ultrasound only showed a superficial clot, she contacted her doctor again. This time, another ultrasound showed that she now had a more dangerous type of clot – a deep vein thrombosis (DVT).

“In a very short time frame, the blood clot had developed into a DVT that almost fully blocked the vein and could have led to a stroke,” says Buckberrough. “Had I ignored the warning signs, or my physician hadn’t responded and acted so quickly, I would have without a doubt faced a very different and potentially life-threatening outcome.” 

“If you start experiencing any or all of the C-L-O-T-S warning signs, do not ignore them – especially if you have multiple symptoms,” adds Dr. Lee.  “As with many illnesses, the sooner you seek medical help, the sooner you can be treated.”

#KNOWTHROMBOSIS is a global campaign to mark World Thrombosis Month (October) and to educate people about the risk factors and warning signs of blood clots.  For more information, visit or @thrombosiscan

Thrombosis Canada acknowledges the generous support from Bayer Canada, Bristol-Myers Squibb Canada/Pfizer Canada Alliance, Pfizer Canada, Leo Pharma Inc and Sanofi Canada in furthering awareness and education initiatives during World Thrombosis Month.