Blood clots are the body’s first aid against bleeding. The blood turns from a liquid into a gel-like state, protecting the flow of blood by plugging any leaks that form.

Without blood clotting, smaller vessels that developed a leak inside the body would keep bleeding. If clotting cannot help to seal cuts, the body loses blood from where it needs it – the tissues and organs.

Clotting that rescues damage is a healthy, vital response to danger. But, when normal body systems are disrupted, internal clots can also form and dislodge, causing medical problems.

Many blood clots occur after surgery. The Centers for Disease Control and Prevention (CDC) say that 50 percent of all blood clots develop “during or soon after a hospital stay or surgery.”

In a paper, published in 2010, it was estimated that blood clots in the veins are “a major public health problem that affects an estimated 300,000-600,000 individuals in the United States each year.”

This article explains the main clot diseases involving the veins:

  1. Deep vein thrombosis (DVT)
  2. Pulmonary embolism (PE)

When blood clots form directly in the arteries, two major medical events can occur. Broadly, clots forming in major arteries lead to:

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A blood clot that forms in an artery can cut the supply of blood to major organs.
  • Heart attack – where the heart muscle has its blood supply cut
  • Stroke – where part of the brain loses blood supply

This article looks at the clotting in the veins that leads to DVT and PE.

A deep vein thrombosis – a clot, usually in a lower leg – is one major cause of pulmonary embolism. It occurs when a DVT travels from the site where it was produced and lodges in the blood supply for the lungs.

Clots lodging in the lungs can also occur in people without a DVT, and an embolism doesn’t happen in all people with a DVT.

The most common place for a blood clot to develop is the legs. In this case, symptoms may include:

  • Pain
  • Swelling
  • A warm sensation
  • Tenderness
  • A reddish, dusky discoloration
  • Pain in the calf when stretching toes upward

Blood clots give differing symptoms depending on where in the body they occur:

  • Blood clot in the heart – chest pain and a sensation of heaviness in the chest; lightheadedness and breathing difficulty
  • Blood clot in the abdomen – vomiting, severe pain in the abdomen.
  • Blood clot in the brain – sudden and intense headache. Cognitive changes, such as difficulty speaking.

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Most cases of DVT occur in the calves.

Gel-like clumps of congealed blood can form in one of the veins, most commonly deep in the leg. This is a deep vein thrombosis (DVT).

According to the CDC, deep vein clots are a serious condition that is underdiagnosed but preventable.

The following may be signs and symptoms of a deep vein thrombosis. For most DVTs, these are in the calf:

  • Swelling
  • Pain
  • Tenderness
  • Redness of the skin
  • Warmness of the skin

The pain can feel like a pulled muscle or heavy ache. Whether or not the symptoms turn out to signal a DVT, they are problems that need the attention of a doctor as soon as possible.

Doctors will be able to investigate the full picture, do more tests, and get treatment started. They may look for more detailed signs of DVT, including:

  • The location and amount of the swelling, and how this compares with the other limb
  • How the tenderness relates to the form of the veins in the leg

Doctors will want to treat or rule out DVT based on other risks. These can include:

  • Cancer or recent treatment of it
  • Paralysis or partial paralysis
  • A leg cast for a fracture
  • Recent long-distance travel, including long-haul flights

The National Blood Clot Alliance have produced a “passport to safety” relating to good tips for helping to prevent DVT, including practical prevention measures including staying hydrated, moving the lower legs, and getting up for a walk.

DVT risk factors

Some diseases raise the chances of a DVT. Cancer is one example. Most cases of DVT happen in people:

  • Whose blood cannot easily get back to the heart because they are unable to move
  • Patients with damaged vein linings because of major muscle trauma, for instance, or from long-term vascular diseases such as diabetes mellitus

Other risk factors for DVT include:

A pulmonary embolism (PE) is a blocked artery in the chest that occurs when a blood clot is pushed along the bloodstream and lodges in the lungs.

DVT and PE are often related, and can sometimes happen together. Doctors will be more alert to the possibility of a PE in anyone with DVT, or who is at high risk of a clot.

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A pulmonary embolism can cause shortness of breath and pain when breathing deeply.

A clot in the lungs produces serious symptoms that need urgent medical attention. PE may be signaled by:

  • Shortness of breath – finding it difficult to get enough breath for no obvious reason
  • Pain when breathing deeply

Other symptoms of PE can include:

  • Fast breathing and a fast heart rate
  • Blood when coughing

Any of the above symptoms need urgent medical attention, whether they are due to PE or not. Other serious symptoms that can go with PE include:

  • Anxiety or dread
  • Collapsing with a light head or fainting
  • Sweating

People should always seek medical help when feeling unwell and concerned.