Blood Clots

Reviewed on 2/3/2022

Facts You Should Know About Blood Clots

A blood clot forming in a artery
Blood clots can form in the legs, lungs, and heart.
  • Blood clots form routinely as a normal function of blood cells to repair damaged blood vessel walls. Blood clots become a problem when the blood "clots" in an artery or vein inappropriately prevent blood from flowing through those blood vessels
  • Risk factors for developing blood clots in arteries include high blood pressure, high cholesterol, diabetes, smoking, and family history of forming blood clots.
  • Risk factors for developing blood clots in veins include prolonged immobility (including immobility after surgery), hormone therapy (including birth control pills), smoking, pregnancy, and genetic factors.
  • Causes of arterial blood clots include atherosclerosis plaques ruptures, as in a heart attack. A clot embolus can block (occlude)  an artery after it travels from one part of the body to another, for example, a stroke can occur from a  blood clot that originates in the heart.
  • Causes of venous blood blots include immobility, where the blood stagnates and begins to clot. For example, a blood clot forms in the leg from lack of activity from prolonged travel in a car, train, plane or being bedridden after surgery.
  • Signs and symptoms of blood clots depend upon their location and whether they occur in an artery or a vein. A blood clot in an artery that supplies blood to the heart or brain may result in
  • When blood clots occur in a vein, symptoms may include
    • pain,
    • swelling,
    • warmth, and
    • redness.
  • If a forms in a vein in a leg or arm breaks off and travels to the lung, it causes  a pulmonary embolus, a potentially life threatening condition can occur. Symptoms of pulmonary embolism are
  • Blood clots are diagnosed initially by history and physical examination. Other tests may be ordered depending upon the location of the blood clot.
  • The treatment for blood clots depends upon the location, but most situations require the use of anticoagulant medications that thin the blood, and prevent further clots.
  • Medications used for blood clot treatment thin or anticoagulate the blood.
  • Complications of blood clots often depend upon their location.
  • Blood clots can be prevented by remaining active, especially after surgery; quitting smoking, especially if a woman takes birth control pills; and life-long control of high blood pressure, high cholesterol, and diabetes.
  • The prognosis for a person with a blood clot depends upon the health of the person, the location of the blood clot, and how quickly medical care is accessed.

What Are Signs and Symptoms of a Blood Clot?

Signs and symptoms of a blood clot depend upon the situation, the amount of bleeding, and the location of the blood clot. Many times, the clot itself may cause no symptoms until it embolizes and becomes lodged in small blood vessels at distant sites in the body. The effects of the lack of blood supply to an affected organ will determine the symptoms.

  • In atrial fibrillation, the clots that form may not cause symptoms unless they embolize.
  • If the clot embolizes to an artery in the brain, the symptoms will be that of stroke.
  • If the embolus involves an artery that supplies blood to the small or large bowel (known as mesenteric ischemia), symptoms may include abdominal pain, nausea, vomiting, and bloody bowel movements.
  • In a leg or arm, a blood clot in a vein (deep venous thrombosis) can act as a dam and block blood from returning to the heart. This may cause inflammation of the vein, or thrombophlebitis. Common symptoms include swelling, redness or discoloration, warmth, and pain.
  • The major complication of a deep venous thrombosis occurs when the clot breaks off and travels to the lung, causing a pulmonary embolism. Symptoms and signs include chest pain, shortness of breath (rapid breathing and a fast pulse). This is a potentially life-threatening condition depending upon the extent of the lung tissue that loses blood supply and the effect it has on both heart and lung function.
  • Signs and symptoms of an arterial clot depend upon which organ is losing its blood supply.
    • If it is located in a coronary artery, there may be signs of heart attack.
    • Cerebral artery occlusion by clot will manifest in signs of stroke.
    • A patient with an arterial clot to an arm or leg will develop a painful, cool, white, pulseless extremity.

How Do Blood Clots Form?

Picture of blood clotting
Picture of blood clotting

Blood flows through the body in a continuous loop. Blood is pumped through the body by the heart, but that same blood returns back to the heart both by gravity and by the muscles of the arms and legs contracting and squeezing, or milking, the blood back to the heart. If blood becomes stagnant, it may clot and cause potential life-threatening conditions.

The medical term for a blood clot is a thrombus (plural: thrombi). An embolus refers to the situation in which the clot breaks away from its original location and travels through the bloodstream to another location.

There are four potential outcomes regarding a blood clot. It will either

  1. grow,
  2. dissolve,
  3. embolize, or
  4. recannulate (a situation in which capillary blood vessels proliferate within the clot to form new channels so that blood may resume flow)

Blood clots that increase in size or embolize may cause limb (arm, leg) or life threatening conditions.

How Do You Get Blood Clots?

Blood is supposed to clot to help repair a blood vessel that is injured. Clots or thrombi become a problem when they form inappropriately. There are a variety of illnesses and risk factors that can lead to blood clot formation.

Blood clots in the heart

Atrial fibrillation describes a heart rhythm disorder in which the upper chamber of the heart does not beat in a coordinated fashion. Instead of having a single electrical impulse that allows the atrium to contract, hundreds of electrical impulses are generated, and the atrium jiggles like a bowl of Jell-O. This may cause small blood clots to form along the lining of the atrium. The potential exists for these clots to break away and embolize to other parts of the body, causing diseases such as stroke or ischemic bowel (loss of blood supply to part of the intestine).

Blood Clots in Veins

Deep vein thrombosis (DVT) is the term used to describe clots that form in the veins of the arms, legs, or major veins in the pelvis. Risk factors for DVT include:

  • Prolonged immobility
  • Surgery to an arm or leg, including casting for a broken bone or trauma
  • Pregnancy
  • Inherited blood clotting disorders
  • Smoking
  • Hormone therapy including birth control pills

Immobility may include recent surgery or hospitalization. This is especially a concern when surgery on a leg is involved or the extremity may be immobilized in a cast or splint. It also includes patients who undergo hip and knee replacement. Muscle movement in the extremity may be decreased, and this lack of motion increases the risk of blood clot formation. Prolonged airplane and automobile trips similarly minimize movement. Blood tends to pool by gravity in the lowest parts of the body. Without standing and walking at regular intervals, blood is not returned easily back to the heart by muscle contraction, and blood clots may form.

Blood Clots in Arteries

Blood clots may form acutely in an artery that has been gradually narrowed by plaque in vessels affected by arteriosclerosis. Plaque is a collection of cholesterol, calcium, fibrin and cell waste products that can form, grow and gradually narrow an artery. If the plaque ruptures, it may initiate the clotting cascade, and a newly formed clot can completely block an artery. The risk factors for arterial clot are those commonly associated with heart attack, peripheral vascular disease, and stroke.

These include:

Blood Clots in Other Areas

When bleeding occurs outside an artery or vein the blood tends to pool and clot. Passing blood clots in the urine, the vagina, or in the stool is very frightening and should not be ignored. There may be a significant problem, or the bleeding may be easily explained. For example, bleeding is commonly seen with bladder infections or hemorrhoids.

Bleeding or blood clots in the urine should not be ignored and presumed to be "just a bladder infection." The bleeding may arise from a bladder tumor or irritation of the bladder lining from other reasons (for example, cancer radiation therapy), or it may originate in the kidneys because of kidney stones or cancer. Sometimes, if there is enough bleeding, clots will form in the bladder and may pass in the urine. This is commonly seen in older male patients with enlarged prostate glands that may cause difficulty with urination.

Blood in the stool or rectal bleeding is never normal and should always be investigated. While hemorrhoids or anal fissures may be the source, bleeding may also be due to a variety of other illnesses including tumors, or cancer, inflammatory bowel disease, infections, and diverticular bowel disease. Again, if there is enough bleeding present, blood clots may form and be passed as part of a bowel movement. Passing blood clots from the vagina happens almost routinely in menstruation. If blood from the uterus pools in the vaginal area, blood clots of varying sizes may form. However, vaginal bleeding during pregnancy is never normal and medical advice should always be accessed if this occurs, either by telephone or in person.

When Should You Call a Doctor if You Think You Have a Blood Clot?

Usually the signs and symptoms of a blood clot will be enough to alert and potentially alarm a patient or their family enough to seek care.

An arterial clot prevents blood rich with oxygen and nutrients from getting to cells, causing them to stop functioning. This usually causes a true emergency and emergency services should be activated (often by calling 911).

  • If those oxygen-deprived cells are in the brain, then symptoms of stroke may be apparent. Time is of the essence in seeking emergency care. There is a narrow time window during which clot-busting drugs may be used to dissolve the blood clot and reverse the stroke. The acronym for symptoms of a stroke are FAST, which stands for:
    • F = drooping face
    • A = arm weakness
    • S = speech difficulty
    • T = time to call 911
  • A heart attack (myocardial infarction) occurs when the blood clot occludes a coronary artery (one of the arteries that supplies oxygen and nutrients to the heart muscle). The signs and symptoms of heart attack include:
  • Again, time is of the essence to try to re-establish blood supply to heart muscle by heart catheterization and balloon angioplasty and stent or by administering clot-busting drugs. The goal is to have the blocked heart artery opened up within 60-90 minutes of the patient's arrival at a medical care facility.
  • Other arterial clots will usually cause an acute onset of significant pain and will signal the need for emergency medical care.

Which Types of Doctors Treat Blood Clots?

Many different health-care professionals may be involved in caring for a person with a blood clot depending on where the clot is, and the patient's medical situation. Specialists that treat blood clots include emergency room doctors; primary health-care professionals including family medicine; internal medicine; women's health professionals; cardiologists; neurologists; pulmonologists; vascular surgeons; hematologists; interventional radiologists; and hospitalists.

How Do Medical Professionals Diagnose Blood Clots?

The first step in making the diagnosis of a blood clot is obtaining a history from the patient for family. Patients rarely are able to make their own diagnosis of a blood clot so the health-care professional will need to ask questions about what might be happening. If a blood clot or thrombus is a consideration, the history may expand to access the patient's risk factors or situations that might have put the patient at risk for forming a clot.

  • Venous blood clots (venous thrombi) often develop slowly with gradual swelling, pain, and discoloration of the involved area, and the signs and symptoms will progress over hours.
  • An arterial thrombus occurs as an acute event. Tissues need oxygen immediately, and the loss of blood supply as a result of an arterial clot creates a situation in which symptoms begin immediately.

Physical examination will help add information to increase the suspicion for a blood clot.

  • Vital signs are an important first step of the physical exam. Blood pressure, heart rate, respiratory rate and oxygen saturation (what percent of red blood cells have oxygen attached to them) may provide a clue as to whether the patient is stable or in potential danger.
  • Venous thrombi may cause swelling of an extremity. It may be red, warm, and tender and sometimes the physical exam may make it difficult to distinguish a venous thrombus from cellulitis or an infection of the extremity. If there is concern about a pulmonary embolus, the examiner may listen to the heart and lungs looking for abnormal sounds caused by an area of inflamed lung tissue, or unusual heart sounds.
  • Arterial thrombus is much more dramatic. If an arm or leg is involved, the tissue may be white because of the lack of blood supply. As well, it may be cool to touch, and there may be loss of sensation and movement. The patient may be writhing in pain, but may not be able to move affected limb. Arterial thrombus is also the cause of heart attack, stroke, and ischemic bowel.

Testing for venous blood clots

Testing will depend on the suspected location of the blood clot.

  • Ultrasound: Venous blood clots may be detected in a variety of ways, although ultrasound is now most commonly used. Occasionally, the patient's size and shape may make it difficult for the ultrasound technician and radiologist to evaluate the deep veins of an arm or leg.
  • Venography: Venography may be another alternative to look for a clot. A radiologist injects contrast dye into a small vein in the hand or foot, and using fluoroscopy (video X-ray) watches the dye fill the veins in the extremity as it travels back to the heart. This test is no longer commonly used, but may be available in certain select circumstances.
  • Blood tests: Sometimes, a blood test is used to screen for blood clots. D-dimer is a breakdown product of a blood clot, and levels of this substance may be measured in the bloodstream. Blood clots are not stagnant; the body tries to dissolve them at the same time as a new clot is being added. D-dimer is not specific for a blood clot in a given area and cannot distinguish the difference between a "good" (necessary) blood clot (one that forms after surgery or due to bruising from a fall) from one that is causing problems. It is used as a screening test in patients with low probability of having a blood clot. In this case, if the result is negative, there is no need to search further for the diagnosis of blood clots.
  • Additional tests: Should a blood clot embolize to the lung, this may be a medical emergency. There are a variety of tests to look for pulmonary emboli. A plain chest X-ray will not show blood clots, but may be done to look for other conditions that can cause chest pain and shortness of breath, the same sings and symptoms of an embolus. The electrocardiogram (EKG) may show abnormalities suggestive of a pulmonary embolus and may also show other reasons for chest pain.

Computerized tomography (CT) is often the test of choice when suspicion of pulmonary embolus is high. Contrast is injected intravenously, and the radiologist can determine whether a clot is present.

On occasion, ventilation perfusion (V/Q) scans are performed to look for pulmonary emboli. This test uses labeled chemicals to identify inhaled air into the lungs and match it with blood flow in the arteries. This test is less accurate than a CT scan and is subjective to variances in interpretation.

Should a pulmonary embolus be diagnosed, the amount of clot and potential severity of the disease may require further testing. Echocardiogram is an ultrasound of the heart that may be used to decide how much strain the blood clot in the lung is causing on the heart.

Testing for arterial blood clots

Arterial thrombosis is an emergency, since tissue cannot survive very long without blood supply before there is irreversible damage. In an arm or leg, often a surgeon is immediately consulted. Arteriography may be considered. Arteriography is a technique in which dye is injected into the artery in question to look for blockage. Sometimes, if there is a large artery that is occluded, this test is done in the operating room with the presumption that a surgical procedure will be necessary to open the vessel and restore blood flow.

For an acute heart attack, the EKG may confirm the diagnosis, although blood tests also may be used to look for enzymes (troponin) that leak into the bloodstream from irritated heart muscle. With an acute heart attack, the diagnostic and therapeutic procedure of choice is a heart catheterization. A catheter is placed into the coronary artery, the blockage identified and a stent placed to restore blood supply to heart muscle.

Other variations of head CT may be considered to look at blood flow in the brain (perfusion CT) or the arteries themselves (CT angiogram).

For an acute stroke (cerebrovascular accident, CVA), the test of choice is a computerized tomography (CT) scan of the head to look for bleeding or tumor as the cause of stroke symptoms. If the stroke symptoms resolve, meaning that a transient ischemic attack (TIA) has occurred, tests may include carotid ultrasound to look for blockage in the major arteries of the neck and echocardiography to look for blood clots in the heart that may embolize to the brain.

What Is the Medical Treatment for Blood Clots?

Depending upon their location, blood clots may be aggressively treated or may need nothing more than symptomatic care.

Venous thrombosis in the leg may occur in the superficial or deep systems of veins.

Clots in the superficial system are often treated symptomatically with warm compresses and acetaminophen or ibuprofen since there is no risk for clots in the superficial veins to embolize to the lung. They are connected to the deep system by perforator veins that have valves that act like a sieve to strain and prevent clots from traveling to the lung.

Deep venous thrombosis usually requires anticoagulation to prevent the clot from growing and causing a pulmonary embolus. Treatment tends to occur in an outpatient setting using medications that anticoagulate or "thin" the blood. There are a variety of medications available to treat blood clots.

  • The American College of Chest Physicians has published guidelines regarding the type of blood thinners to be considered in the treatment of blood clots in the legs or in the lungs.
    • In patients with DVT or PE and no active cancer, the drug of choice is a novel oral anticoagulant (NOAC), also known as a direct oral anticoagulant (DOAC) because of where they block the coagulation cascade to thin the blood.
  • NOACs that block clotting Factor Xa include:
    • apixaban (Eliquis)
    • rivoroxiban (Xarelto)
    • edoxiban (Savaysa)
    • dabigatran is another NOAC that is a direct thrombin inhibitor.
  • In patients with DVT or PE and active cancer, the recommended medication is low molecular weight heparin or enoxaparin (Lovenox).
  • In unstable patients, or those where there is concern that they will become unstable in the near future, and who need hospitalization, the anticoagulation drug that is recommended is intravenous unfractionated heparin. When there is a large amount of blood clot in the pulmonary arteries, strain can be put on the heart and lung function and thrombolytic therapy with tissue plasminogen activator (tPA) drugs, so-called clot busting drugs, might be considered. These patients are usually critically ill and in shock.
  • If there is massive amount of clot in the femoral or iliac veins, no blood may be able to leave the leg and it becomes massively engorged, swollen and blue. This is called phlegmasia cerulia dolens and may require treatment with tPA. Similar situations may occur in the arm with clots that form in the subclavian or axillary vein.
  • Classically, warfarin (Coumadin) was most commonly used to treated blood clots. It is a vitamin K inhibitor and affects Factors II, VII, IX and X of the clotting cascade. Because it takes a few days to reach therapeutic levels, an injectable heparin product, (enoxaparin, fondaparinux) was also prescribed for the patient as a bridge to immediately thin the blood.

Blood clots below the knee are at lower risk for embolization to the lung, and an alternative to anti-coagulation treatment is serial ultrasound examinations to monitor the clot to see whether it is stable or growing.

Pulmonary emboli are treated similarly to deep venous thrombosis. In patients who have increasing shortness of breath or weakness, hospitalization may be required during the initial treatment phase. In certain situations, when there are large amounts of blood clot in the pulmonary arteries, strain can be put on the heart and lung function and thrombolytic therapy with tissue plasminogen activator (tPA) drugs, so-called clot busting drugs, might be considered. These patients are usually critically ill and in shock.

Arterial blood clots are often managed more aggressively. Surgery may be attempted to remove the clot, or medication may be administered directly into the clot to try to dissolve it. Alteplase (Activase, tPA) or tenecteplase (TNKase) are examples of clot busting medications that may be used in peripheral arteries to try to restore blood supply.

Heart attack: The same approach for heart attack is used as for arterial blood clots. If possible, cardiac catheterization is performed to locate the blocked blood vessel and a balloon is used to open it, restore blood flow, and a stent is placed to keep it open. This is a time-sensitive procedure and if a local hospital is unable to perform a heart catheterization emergently, within 60-90 minutes of the patient's arrival to medical care, thrombolytic medications described above like tPA or TNK may be used intravenously to try to dissolve the thrombus and minimize heart muscle damage. There will still be the need to eventually transfer the patient when stable to a hospital with the capability to perform heart catheterizations.

Stroke also is treated with tPA if the patient is an appropriate candidate for this treatment. Each patient is different and may or may not qualify for this medication with an acute stroke. Again, this is a time sensitive emergency and in addition to tPA, an interventional radiologist may be able to insert a catheter into the blood vessels of the brain, identify the clot and remove it, thus hopefully reversing the stroke.

What Medications Treat Blood Clots?

The treatment of blood clots often is directed at interfering with the normal clotting mechanism of the body. Different medications may be used to block specific factors in the clotting cascade and are chosen based upon the disease or illness being treated and other underlying medical issues that are present in the individual patient. Some of the medications prevent additional or future blood clots while others can help dissolve existing blood clots.

Aspirin is commonly used to decrease platelet function (platelets are important in helping clot formation) in the treatment of heart attack and stroke. Other anti-platelet drugs include clopidogrel (Plavix), prasugrel (Effient), ticagrelor (Brillanta), ticlopidine (Ticlid) and aspirin and dipyridamole (Aggrenox).

Warfarin (Coumadin) acts as a blood thinner by blocking clotting factors (II, VII, IX and X) that depend upon vitamin K. Every patient is unique when it comes to the dosing requirements for warfarin (Coumadin), and repeat blood tests are routinely done to make certain that the blood is anti-coagulated to the appropriate level. There are numerous drug interactions with this medication that can cause the blood to become "too thin" such as some antibiotics. Warfarin (Coumadin) dosing always needs to be monitored by a healthcare professional, and a patient should never alter the dose of this medication without consulting with their healthcare professional.

Factor Xa inhibitor medications have been approved for the treatment of certain types of atrial fibrillation, deep venous thrombosis and pulmonary embolism. They begin working almost immediately and do not need blood tests to monitor their activity. Medications in this class of anticoagulants include apixaban (Eliquis), rivaroxaban (Xarelto), and edoxaban (Savaysa). Dabigatran (Pradaxa) also is an alternative anticoagulation medication that is a direct thrombin inhibitor. As opposed to warfarin, which can have its anticoagulation activity reversed, at present there is no reversal agent available in the United States for Factor Xa and thrombin inhibitor medications. These medications also may be used to help prevent blood clots in the leg after hip and knee replacement surgery.

Heparin works by inactivating thrombin and factor X. It is an injectable medication available for use intravenously or as a low molecular weight medication called enoxaparin (Lovenox) or fondaparinux (Arixtra), which can be injected subcutaneously (under the skin). Heparin is often used routinely as part of the heart attack treatment protocol. Because of its rapid onset of action it is often the first medication started once a blood clot is diagnosed in the hospital.

Tissue plasminogen activator (tPA or TNK) may be used to dissolve blood clots that are life-threatening and are most often used for clots that occlude arteries in situations such as stroke or heart attack; there are occasional instances in which the drug is used for major vein obstruction. The medication can be injected into an intravenous line that has been started in a vein of the arm, or it may be dripped directly into the clot. This requires specialized critical care technology and physician skill to thread a catheter to the site of blockage to deliver the clot-busting medication. Decisions regarding the use of this drug are individualized for the specific patient and situation.

Are There Any Natural Cures or Home Remedies for Blood Clots?

Recognizing that a potential illness may exist associated with a blood clot is the first step in getting treatment. Since many of these illnesses are life-threatening (heart attack, stroke, pulmonary embolus, ischemic bowel), accessing emergency care and calling 911 may be the most important step in treatment.

What About Surgery for Blood Clots?

Depending upon the underlying disease, surgery may be required to remove a blood clot. Often this occurs emergently in life- or limb-threatening situations in which anti-coagulation with heparin or the use of thrombolytic medications is not appropriate or when these have failed to resolve the blood clot.

What Is the Prognosis for a Person with a Blood Clot?

There are many patients who don't know that they have had a blood clot in their leg, either because the symptoms were mild, or those symptoms were ignored. Up to 25% of patients with a pulmonary embolus die from sudden death.

For those patients with a provoked deep vein thrombosis, one where the cause is known and is temporary, there is a small risk of future bloods clot once the initial anticoagulation treatment is complete.

For patients who have an unprovoked DVT or PE or who have active cancer or a blood clotting disorder that makes their blood more likely to clot, lifelong anticoagulation may be required. Guidelines suggest that this decision be revisited every year.

For all patients, the patient and the health-care professional need to balance the benefit of anticoagulation against the complication risk of bleeding. The doctor will try to match the blood thinning drug with the patient's situation, to minimize that risk of bleeding.

Is It Possible to Prevent Blood Clots?

Prevention is always the key in medicine. This is especially true when it comes to many of the diseases associated with blood clots.

  • Risks of arterial blood clots associated with heart disease, stroke, and peripheral artery disease may be minimized by keeping high blood pressure, diabetes, and cholesterol levels under control. Smoking cessation should be a priority.
  • Deep vein thrombosis and pulmonary embolus prevention is a priority in hospitalized patients. Often those undergoing surgery are aggressively encouraged to start walking as early as possible, and medications may be used prophylactically to prevent clot formation.
  • Travelers should be encouraged to get up, stretch, and walk routinely. This is especially true on long airplane trips or long car rides.
  • Hormone therapy is a risk for blood clot formation, and smoking compounds that risk. People who choose to smoke should notify their health-care professional; the benefits of birth control and/or hormone therapy will need to be balanced against the risk of complications.

Deep Vein Thrombosis (DVT) Symptoms and Signs

Symptoms of a blood clot in the leg (deep vein thrombosis or DVT) occurs when a clot clogs the blood flow in a vein, causing inflammation. Examples of symptoms and signs of a DVT in a leg are:

  • Swelling
  • A gradual onset of pain
  • Redness
  • Leg cramps...
Reviewed on 2/3/2022
Guyatt, Gordon H., et al. "Executive Summary: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines." Chest 141(2_suppl) Feb. 2012.