What are the signs and symptoms of blood clots?

What are the signs and symptoms of blood clots?

Not all occurrences of blood clots will show signs of noticeable physical distress. When any signs do become noticeable it is important to seek medical attention as soon as possible. (5)

The most common warning signs of a clot in the venous (vein) system / venous thromboembolism (which can mimic those of an infection) include:

  • Oedema (swelling) – elevation or cold compresses will not likely reduce swelling in the case of a blood clot, as it would do in instances of muscle injury.
  • Warm sensations (near the site of the clot / general area which may also sometimes be itchy)
  • Inflammation or redness on the skin surface (in and around the affected area)
  • Pain and or / tenderness (likened to a muscle cramp or charley horse – a sudden involuntary muscle contraction / spasm)
  • Skin discolouration (red, bluish or blanching / pale)

Blood clots that occur in the deeper veins of the body effectively prohibit the flow of blood back to the heart. Such symptoms are often experienced in the legs or arms over the course of a few hours and vary in severity depending on the size of the thrombus. Most often, symptoms affect one area, such as one arm or leg, or side of the pelvis (clots affecting both limbs at the same time, for instance are very rare). A large clot may cause extensive swelling and pain in, for instance the entire leg, as opposed to just the calf area.

Signs of blood clots which have formed in the body’s arteries 

Clots in the arteries can quickly become dangerous as blood is not able to be pumped to an affected area, which in turn deprives tissues of essential oxygenated blood supply (known as ischemia). Tissues then effectively begin to sustain damage and die, often resulting in a medical emergency. 

Signs of an arterial blood clot often depend on its location in the body:

  • Coronary arteries (chest area i.e. myocardial infarction / heart attack): Indigestion, nausea, sweating, pressure in the chest (likened to a heavy feeling – an elephant sitting on the chest) or chest pain (angina), shortness of breath, rapid heart rate, cough, light-headedness (or loss of consciousness), numb or cold sensations (i.e. in the left arm), and sharp pain which radiates from the centre to the jaw, arm or back – on the left side (signs of possible heart attack).
  • Arteries in the brain (or carotid arteries in the neck): Sudden headache, loss of vision (visual disturbances), impaired, difficulties with or loss of speech, loss of concentration, body weakness (especially in the arms), difficulties with movement or walking, loss of sensation in the body (especially on one side, such as the limbs), facial drooping or seizures and loss of consciousness (signs of possible stroke or transient ischemic attack, known as a ‘mini stroke’ or TIA). Blood clots may develop in the brain as a result of fatty deposits in the walls of blood vessels supplying blood to the brain. Alternatively, a head injury that results in a concussion can also lead to the formation of a thrombus. (6) Clots may form in the chest or neck area and also travel to the brain via the bloodstream, and potentially cause a stroke. 
  • Mesenteric ischemia (abdominal area – mesenteric thrombosis): These arteries supply blood to the intestine. If a clot occurs it can cause severe abdominal pain (especially if this continually worsens or becomes more acute after eating), nausea and vomiting, swelling (bloating), diarrhoea and blood in the stool (faeces) or vomit – potential signs of mesenteric ischemia.

Pulmonary embolism

Signs that a blood clot has reached the lungs (signs of a pulmonary embolism / PE) include:

  • Sudden shortness of breath (even when at rest and not in an active state)
  • A rapid heart rate / pulse
  • Heart palpitations (an awareness of heart beats)
  • Fever
  • Excessive sweating
  • Chest pain (sharp)
  • Breathing difficulties (chest pain may worsen when inhaling or coughing causing breathing problems)
  • Coughing up of blood (bloody phlegm)
  • Light-headedness or dizziness
  • Loss of consciousness

Blood clot in kidney

Signs that a blood clot is affecting the kidneys include:

  • Fever
  • Nausea and / or vomiting
  • Pain in the abdomen, thighs and / or lower legs
  • Hypertension
  • Blood in the urine
  • Sudden swelling in the legs
  • Breathing difficulties

Signs of a clot in the kidneys can become severe and cause serious complications, such as problems with removing waste from the body and kidney failure (7).

Knowing the warning signs can sometimes mean the difference between life and death. A clot that is mobile can quickly cause serious complications in the heart, lungs or brain. It’s important to recognise a combination of signs which can indicate the presence of a clot and act swiftly to ensure that a prompt medical diagnosis is made and the most effective treatment administered.

Bruised knee of a woman (close-up).

Bruise or blood clot?

Like blood clots, bruises (also known as contusions) involve blood abnormalities or injury which results in noticeable discolouration of the skin. A bruise effectively forms when injury or trauma occurs on the skin, or blunt force contributes to a fracture (broken bone).

Other risk factors for bruises include:

Capillaries, which are small blood vessels beneath the skin's surface burst and trap blood in the affected area. 

Bruises may be painful, mildly uncomfortable, tender or sore, or result in no symptoms at all. Skin takes on a bluish or dark purple / black colour as a result of a lack of oxygenated blood being delivered to the affected area. During healing, bruises take on other colours such as red, green and yellow before completely returning to normal (i.e. disappearing). As discolouration fades, so too does any discomfort or pain.

Bruises may occur just beneath the skin's surface (known as subcutaneous bruises), in the muscles or even in the bones (known as periosteal bruises). Symptoms of a bruise are generally consistent with each occurrence, no matter where on the body it occurs. 

Discolouration due to a blood clot will likely be accompanied by associated symptoms of the location of the thrombus (i.e. leg, arm, chest, abdomen, head etc.). Bruising is only worrisome when a cause is unknown and it is accompanied by severe swelling and pain or other symptoms. Bruising can also lead to the development of a blood clot. In this case, medical intervention is necessary to determine an underlying problem causing bruising as a symptom. 

For the most part, bruising is not a major concern and can be remedied with a little cold compress, followed by a warm one to reduce inflammation or discomfort. Blood clots which are noticeable with skin discolouration have more serious consequences and do require medical intervention, as soon as possible. 


5. National Heart, Lung and Blood Institute. Venous Thromboembolism: https://www.nhlbi.nih.gov/health-topics/venous-thromboembolism [Accessed 28.08.2018]

6. Centers for Disease Control and Prevention. March 2017. What are the Signs and Symptoms of Concussion?: https://www.cdc.gov/traumaticbraininjury/symptoms.html [Accessed 28.08.2018]

7. MedlinePlus. August 2018. Acute arterial occlusion - kidney: https://medlineplus.gov/ency/article/001272.htm [Accessed 28.08.2018]

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