Blood clots: symptoms, diagnosis and treatment explained

Your blood’s clotting ability is important to help stop excessive and potentially dangerous bleeding when a blood vessel is injured. However, blood clots can form inappropriately and cause a thrombus, where the clot reduces blood flow through a vessel — this can be potentially life-threatening. 

When blood clots don’t break down, they can lead to serious medical conditions. They can form in blood vessels in any part of your body, causing pain and swelling, as well as serious conditions such as heart attacks and stroke

Understanding what blood clots are and which symptoms to look out for can help keep you and others safe in the event that a harmful blood clot forms.

What are blood clots?

A blood clot is blood that has changed from its liquid state to a semi-solid or gel-like clump. Normally, a blood clot would break up and dissolve as part of the healing process, however, this doesn’t always happen.

When a clot forms in a vein or artery, it doesn’t always break up. While a blood clot that doesn’t move won’t usually cause harm, there is a chance that it will break free and travel through your blood vessels. Once the clot is in your veins, it can travel to your lungs or your heart, where it can get stuck and stop blood flow.

When a clot forms in an artery, which carries oxygen in your blood to the cells of your body, it can stop oxygen from getting to your brain, heart or lungs. This is also life-threatening and can cause a stroke or heart attack.

How do you know if you have a harmful blood clot?

As harmful blood clots can affect different parts of your body, the signs that you may have one can vary.

Blood clots in your legs and arms

Blood clots are most likely to form in your legs, especially if you’re sitting down for long periods, such as when you’re driving long distances, taking a flight or have had surgery. However, they can also form in your arms. In either case, they tend to form in deep veins, which is why they’re referred to as a deep vein thrombosis (DVT).

DVT can result in a blood clot travelling to your heart or your lungs; in your lungs it can cause a pulmonary embolism (PE), which is life-threatening. If you have signs of a DVT, seek urgent medical attention.

DVT symptoms include:

  • Colour change — your arm or leg may take on a red or blue tinge
  • Cramps in your leg or arm
  • Pain or itching — you may experience a dull ache, throbbing or intense pain in your arm or leg, which may get worse; you may also feel itchy
  • Pitting oedema — a sudden build-up of fluid in your arm or leg, which when pressed, forms a dimple or pit that stays for several seconds
  • Swelling where the clot has formed or across your entire leg or arm — if your veins swell they may become more prominent and painful, with the pain increasing when you touch them

If you experience trouble breathing it may be a sign that the clot has moved from your arm or leg to your lungs, causing a pulmonary embolism — you should get medical attention immediately.

Blood clots in your heart

If a blood clot forms in or around your heart, or if one travels to your heart, it can lead to a heart attack. Signs of a heart attack include:

  • Difficulty breathing
  • Severe pain in your chest and left arm
  • Sweating

If you experience these symptoms, call 999 or go straight to A&E.

Blood clots in your lungs

In most cases, blood clots in your lungs have travelled there from your arm or leg. As mentioned earlier, this is called a pulmonary embolism (PE) and is a medical emergency.

Signs of a pulmonary embolism include:

Blood clots in your brain

Blood clots in your brain can occur for several reasons, including a head injury or blow to your head, as well as fatty deposits in the walls of the blood vessels that supply your brain. They can also travel to your brain from other parts of your body. Blood clots in your brain can cause a stroke.

Signs of a blood clot in your brain include:

  • A seizure
  • Muscle weakness
  • Speech problems
  • Vision problems

Blood clots in your intestines

Blood clots can also form in the veins that drain blood from your intestines. This type of blood clot can be caused by certain medications, such as the contraceptive pill, or as a result of medical conditions such as liver disease or diverticulitis. 

You should talk to your GP as soon as possible if you experience any of these symptoms:

Blood clots in your kidneys

Your kidneys remove waste from your body and blood clots can stop them from doing this. The result can be kidney failure – if you experience any of the following symptoms you should seek urgent medical attention:


A person checks their blood pressure

How are blood clots diagnosed and treated?

As well as a physical examination, your doctor may send you for a blood clot test. This may include: 

As blood clots can cause symptoms associated with other conditions, you may also have other tests to rule out other causes. 

If you’re diagnosed with a blood clot, the type of treatment will depend on the type of clot you have.

Arterial blood clots

With this type of clot, you may need catheter-directed thrombolysis. This is where medications are delivered to the site of the clot to break it up. Alternatively, surgery may be needed to remove the clot.

As arterial clots can block blood flow to vital organs, emergency treatment is often needed.

Venous clots

If you have deep venous clots ie blood clots in your veins, you’ll likely be given blood-thinning medication. This will prevent the blood clot from getting larger, while your body breaks it down and will prevent more blood clots from forming.

If you’re at high risk of this type of clot, you may need to have a procedure called an inferior vena cava filter placement. This is when a filter is placed in your vein to stop clots from travelling to your heart or lungs.

Who is at risk from blood clots?

While blood clots can affect anyone, there are several risk factors that may increase your risk:

  • Being overweight
  • Having previously had a blood clot
  • Inflammatory conditions eg rheumatoid arthritis or Crohn’s disease
  • Pregnancy or having recently given birth
  • Smoking
  • Taking combined hormonal contraception (the pill, contraceptive patch or vaginal ring)

You’re also more likely to develop a blood clot after a hospital stay.

How can you prevent blood clots?

If you’re at risk of blood clots or if you’re going to be in a stationary position for an extended period of time, such as on a flight or after surgery, there are several ways you can reduce the risk of developing blood clots: 

  • Drink plenty of water
  • Lose excess weight
  • Stay active
  • Wear compression socks or stockings to improve blood flow

If you’re concerned about your risk of blood clots, talk to your GP who can discuss possible treatments to prevent clots with you. 

We hope you've found this article useful, however, it cannot be a substitute for a consultation with a specialist

If you're concerned about symptoms you're experiencing or require further information on the subject, talk to a GP or see an expert consultant at your local Spire hospital.

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Author Information

Cahoot Care Marketing

Niched in the care sector, Cahoot Care Marketing offers a full range of marketing services for care businesses including: SEO, social media, websites and video marketing, specialising in copywriting and content marketing.

Over the last five years Cahoot Care Marketing has built an experienced team of writers and editors, with broad and deep expertise on a range of care topics. They provide a responsive, efficient and comprehensive service, ensuring content is on brand and in line with relevant medical guidelines.

Their writers and editors include care sector workers, healthcare copywriting specialists and NHS trainers, who thoroughly research all topics using reputable sources including the NHS, NICE, relevant Royal Colleges and medical associations.

The Spire Content Hub project was managed by:

Lux Fatimathas, Editor and Project Manager

Lux has a BSc(Hons) in Neuroscience from UCL, a PhD in Cellular and Molecular Biology from the UCL Institute of Ophthalmology and experience as a postdoctoral researcher in developmental biology. She has a clear and extensive understanding of the biological and medical sciences. Having worked in scientific publishing for BioMed Central and as a writer for the UK’s Medical Research Council and the National University of Singapore, she is able to clearly communicate complex concepts.

Catriona Shaw, Lead Editor

Catriona has an English degree from the University of Southampton and more than 12 years’ experience copy editing across a range of complex topics. She works with a diverse team of writers to create clear and compelling copy to educate and inform.

Alfie Jones, Director — Cahoot Care Marketing

Alfie has a creative writing degree from UCF and initially worked as a carer before supporting his family’s care training business with copywriting and general marketing. He has worked in content marketing and the care sector for over 10 years and overseen a diverse range of care content projects, building a strong team of specialist writers and marketing creatives after founding Cahoot in 2016.