They are usually beneficial, but they can be harmful

By Heidi Moawad, MD 

 Medically reviewed by Kimberly Brown, MD

Blood clots form to stop excess bleeding from an injury. Usually, blood clots are beneficial but they can be harmful at times, blocking blood flow within the body’s organs, and potentially causing serious consequences, such as a heart attack or a stroke.

In an emergency, the effects of a blood clot can often be treated with medication or surgery. If you have a condition that makes you prone to blood clots, a healthcare provider may prescribe medication to prevent them.

This article will explore the symptoms of blood clots, common causes, diagnostic tests, treatments, and when to see a healthcare provider.

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Symptoms of Blood Clots

Blood clots can cause various symptoms depending on where they form in the body. They can reduce or block blood flow for a few seconds or longer. 

A blood clot can affect any area of the body, but some regions are more susceptible to blood clots than others. 

The most common symptoms and regions of a blood clot are:

  • In the arms or legs: Deep vein thrombosis (DVT) causes swelling in the affected limb.

  • In the heart: A heart attack can cause shortness of breath, chest pain, arm pain, jaw pain, or indigestion.

  • In the brain: A stroke or transient ischemic attack (TIA) can cause vision or language impairments, as well as numbness or weakness on one side of the face or body.

  • In the intestines: Intestinal ischemia can cause abdominal cramping, pain, and digestive problems.

  • In the kidneys: A blood clot in the kidney can cause loss of kidney function, which may cause decreased urination, blood in the urine, and electrolyte imbalances (minerals in the blood, including sodium and potassium).

  • In the lungs: A blood clot in the lungs is called a pulmonary embolism (PE), and it causes shortness of breath and difficulty breathing.

Types of Blood Clots


Blood clots can form at the location of an injury or in a blood vessel such as an artery, vein, or capillary. Clots in blood vessels can be thrombotic or embolic, as follows:

  • A thrombosis is a blood clot that forms in a blood vessel, interfering with blood flow in the vessel where it has formed. 

  • An embolism is a blood clot that has ruptured from its original location and traveled within the blood vessels to block flow in a different location (usually a narrower branch of the blood vessel).

Causes of Blood Clots

The process of blood clot formation involves platelets and proteins. Platelets are a type of blood cell produced in the bone marrow. Injuries, such as a cut, trigger the accumulation of platelets and coagulation (blood clotting) proteins to close off a wound, which prevents blood loss and gives the injured area a chance to heal.1

Harmful blood clots, such as blood clots in the heart’s blood vessels or the peripheral blood vessels (those not in the chest or abdomen), can form due to diseases that provoke atherosclerosis, tissue injury, inflammation, or an abnormality of the blood clotting process.2 Atherosclerosis is a type of damage inside the blood vessel walls. 

Risk factors for harmful blood clots include: 

  • Smoking 

  • Chronic high blood pressure (hypertension)

  • High levels of triglycerides and low-density lipoprotein (LDL) cholesterol (considered "bad" cholesterol) in the blood 

  • Low levels of high-density lipoprotein (HDL) cholesterol (considered "good" cholesterol) in the blood 

  • Uncontrolled diabetes 

  • Atrial fibrillation (an abnormal heart rhythm)3

  • Obesity 

  • Cancer3

  • Blood clotting disorders, such as factor V Leiden deficiency or antiphospholipid syndrome

  • Myeloproliferative disorders (disorders that produce excess blood cells), such as polycythemia vera4

  • Chronic inflammatory diseases, such as systemic lupus erythematosus (SLE)

Each of these conditions has its own treatment. Often, when these conditions are treated, the risk of blood clots is reduced.  

Temporarily Elevated Risk 

Some conditions can increase the risk of a blood clot for a short time until the condition resolves.

These conditions include:1

  • Septicemia or sepsis (a severe bacterial infection throughout the body)

  • Pregnancy

  • After surgery

  • Bone fracture 

  • Major physical trauma with extensive bleeding

  • During hospitalization, due to immobility

Sometimes treatment is used to prevent a blood clot. For example, during hospitalization, some people are given low-dose injections of heparin to prevent a DVT.5

What Medications Can Cause Blood Clots? 

Certain medications may increase the risk of blood clots:6

  • Chemotherapy

  • Estrogen treatments, including hormone replacement therapy and hormonal birth control

Medical treatments that manage excess bleeding, such as vitamin K infusion, could increase the risk of a blood clot. 

Complications and Risk Factors Associated With Blood Clots

To survive, each cell in the body needs oxygen and glucose, which are supplied by the blood. Ischemia is a lack of blood supply to an area of the body, and it prevents the cells from functioning the way they should. The effects of ischemia may resolve within a few seconds if the blood flow is restored.

If a blood clot continues to block blood flow to an area of the body, an infarction can occur. An infarction is tissue damage that occurs due to insufficient blood supply. It can permanently affect the way an organ functions. 

For example:

  • An infarction in the heart may cause heart muscle damage, which can impair the heart’s ability to pump, causing heart failure. 

  • A brain infarct causes a stroke, potentially with permanent weakness in one side of the body, difficulty speaking, or loss of vision. 

  • A PE can permanently damage an area of the lung, causing chronic breathing difficulty. 

  • An intestinal infarction can cause a portion of the intestine to become necrotic (dead), and this would need to be resected (surgically cut away), usually with the formation of a colostomy or ileostomy (the contents of the intestine exit through an opening created in the abdominal wall, where feces is collected). 

  • Post-thrombotic syndrome can occur after a DVT, and the blood vessel involved may be susceptible to clots in the future.2

How to Treat Blood Clots

Treatment of blood clots can include several phases. Initially, you might need lifesaving treatment. This can include things like supplemental oxygen if you have a PE.

You may also need medication to dissolve the blood clot. Depending on the location and severity of the clot and whether it’s life-threatening, you might receive oral or intravenous (IV, in a vein) medication, or you might have medication injected directly into the artery near the clot with an interventional procedure. 

The immediate effects of different types of blood clots are treated differently. For example, medication to control the heart rate might be given for a heart attack, and medication to prevent brain edema (swelling) would be given for a stroke. These treatments can help prevent permanent tissue damage as the blood flow is restored.

Prevention 

If you are at risk of blood clots, you might need ongoing therapy to prevent them. Many different medications are used to prevent blood clots. The right treatment for you may depend on your specific risk factors, your overall health, and other medications you're taking.

A few of the preventative medications include:5

  • Aspirin

  • Coumadin (warfarin)

  • Eliquis (apixaban)

  • Plavix (clopidogrel)

  • Xarelto (rivaroxaban)

Additionally, your healthcare provider would also prescribe treatment for any underlying conditions that you have that could be increasing your risk of blood clots.

Are There Tests to Diagnose the Cause of Blood Clots? 

If you develop signs and symptoms of a blood clot, you would need to have tests to identify the location of the blood clot. After discussing your symptoms with you and doing a physical examination, your healthcare provider might order additional tests. 

Tests you may need include:

  • Blood tests: Can detect changes in platelet count, signs of inflammation, and possibly blood markers of a heart attack6

  • Ultrasound of the extremities: Can visualize a DVT

  • Electrocardiogram (ECG or EKG): Can detect signs of a heart attack

  • Brain imaging: Can visualize a stroke

  • Ventilation/perfusion (V/Q) scan: Can visualize signs of a PE

  • Abdominal computerized tomography (CT): Can visualize signs of intestinal infarction

Your symptoms, medical history, and physical examination would determine the tests you would need. After the initial tests to find a blood clot, you would need diagnostic testing to determine whether there is lasting tissue damage and any underlying conditions that need to be treated. 

When to See a Healthcare Provider 

The immediate effects of a blood clot are nonspecific and can occur due to several different medical reasons.

You should get immediate medical attention if you develop any symptoms that could be associated with a blood clot. 

These include:

  • Swelling of your arm or leg 

  • Shortness of breath 

  • Chest pain 

  • Vision changes, trouble speaking, or weakness or sensory changes on one side of the face or body 

  • Severe abdominal pain 

You will likely need diagnostic tests to determine the underlying cause of your symptoms. Sometimes the timing may provide clues that a blood clot caused the symptoms, but that’s not always the case. 

Summary 

Blood clots are an important part of healing and prevention of excessive blood loss after an injury. However, harmful blood clots can be a serious medical problem, causing a heart attack, stroke, PE, intestinal ischemia, and more.

Numerous factors can increase the risk of blood clots, including hypertension, smoking, inflammatory disease, and more. If you have risk factors, your healthcare provider may prescribe treatment to lower your chances of having a blood clot.

Sources

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Lu M, Qi X, Bi J, Li Y. Impact of the post-thrombotic syndrome on the arterial wall of the lower limbs. Clin Appl Thromb Hemost. 2022;28:10760296221117473. doi:10.1177/10760296221117473

Falanga A, Leader A, Ambaglio C, et al. EHA guidelines on management of antithrombotic treatments in thrombocytopenic patients with cancer. Hemasphere. 2022;6(8):e750. doi:10.1097/HS9.0000000000000750

Tashi T. Hematocrit, White blood cells, and thrombotic events in the veteran population with polycythemia vera. Fed Pract. 2022;39(Suppl 2):S43-S46. doi:10.12788/fp.0243

Bonsu KO, Young S, Lee T, Nguyen H, Chitsike RS. Adherence to antithrombotic therapy for patients attending a multidisciplinary thrombosis service in Canada - A cross-sectional survey. Patient Prefer Adherence. 2022;16:1771-1780. doi:10.2147/PPA.S367105

Wang Y, Liang X, Wang S, et al. Analysis of the risk factors for elevated D-dimer level after breast cancer surgery: A multicenter study based on nursing follow-up data. Front Oncol. 2022;12:772726. doi:10.3389/fonc.2022.772726

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By Heidi Moawad, MD
Heidi Moawad is a neurologist and expert in the field of brain health and neurological disorders. Dr. Moawad regularly writes and edits health and career content for medical books and publications.