Blood clots (DVT and PE): Full guide

What are DVT and PE?

Blood is meant to clot when you are cut, so you stop bleeding. Sometimes a clot forms inside a vein when it should not. This can block blood flow.

A deep vein thrombosis (DVT) is a clot in a deep vein, most often in the leg. It can cause swelling, pain, warmth, or redness in one leg. Sometimes it causes no symptoms at all.

A pulmonary embolism (PE) happens when a piece of clot breaks off and travels to the lungs. It can cause sudden shortness of breath, chest pain, a fast heartbeat, or coughing up blood. A PE can be life threatening and needs care right away.

Doctors use the term venous thromboembolism (VTE) to mean DVT, PE, or both. VTE is common. It is not a cancer.

Clots tend to form for three main reasons. Blood flow slows down, for example when you sit still for a long time or stay in bed after surgery. A vein wall gets damaged. Or the blood clots too easily. Many people have more than one of these at the same time.

With treatment, most clots stop growing, and your body slowly breaks them down. Blood thinners do not dissolve the clot directly. They keep it from growing and stop new clots while your body heals.

Types of clots

Deep vein thrombosis (DVT)

A clot in a deep vein, usually in the thigh, calf, or pelvis. Clots higher in the leg are more likely to travel to the lungs than small clots in the calf.

Pulmonary embolism (PE)

A clot that has traveled to the blood vessels of the lungs. It can range from small and found by chance on a scan to large and very dangerous.

Provoked clot

A clot linked to a clear, short-term trigger, such as major surgery, an injury, a hospital stay, pregnancy, or estrogen pills. When the trigger is gone, the risk of another clot is lower. Treatment is often about 3 months.

Unprovoked clot

A clot with no clear trigger. The chance of another clot after stopping blood thinners is higher. Your care team may suggest staying on a blood thinner long term if your bleeding risk is low.

Cancer-related clot

Cancer and some cancer treatments make clots more likely. About 1 in 5 clots happen in people with cancer. These clots usually need at least 6 months of treatment, often longer while the cancer is active.

Arm clot and catheter clot

Clots can form in the arm, often around a long-term IV line (catheter or port). They are usually treated with a blood thinner, often while the line stays in place.

Clots in unusual places

Clots can form in veins of the belly (liver, spleen, or bowel) or the brain. These need special testing, such as a check for blood disorders like an MPN or PNH.

Recurrent clot

A clot that comes back. Having one clot is the strongest risk factor for another. A second unprovoked clot usually means long-term treatment.

Tests you may have

D-dimer blood test

D-dimer is a piece of a broken-down clot. A normal result in a person at low risk makes a clot very unlikely. A high result is not specific, because it can rise with age, infection, pregnancy, surgery, or cancer.

Leg ultrasound

Sound waves create a picture of the veins. The technician presses gently on the veins to see if they squeeze shut. A vein with a clot does not. This is the main test for DVT.

CT pulmonary angiogram (CTPA)

A CT scan with contrast dye given through an IV. It shows the blood vessels in the lungs. This is the main test for PE.

V/Q scan (lung scan)

A nuclear scan that compares air flow and blood flow in the lungs. It is used when CT contrast dye is not a good choice, such as with kidney problems or a dye allergy.

Heart tests for PE

An echocardiogram (heart ultrasound) and blood tests called troponin and BNP show whether the PE is straining the right side of the heart. This helps decide how serious the PE is.

Blood counts, kidney, and liver tests

These help your care team choose the safest blood thinner and dose. Some blood thinners are not safe with severe kidney or liver disease.

Cancer screening

After an unprovoked clot, your care team may check that your routine cancer screening is up to date. This includes tests such as colon, breast, and cervical screening. Extensive scans looking for hidden cancer are usually not needed.

Clotting disorder tests (only for some people)

Blood tests for inherited or acquired clotting problems are not needed for most people. They may help in some cases. Examples are an unprovoked clot at a young age, a strong family history, repeat clots, or clots in unusual places.

How serious it is

Doctors judge how serious a clot is by where it is, how big it is, and how it affects your heart and breathing.

For a PE, doctors look at your blood pressure, heart rate, oxygen level, other health problems, and heart tests. Scores such as sPESI help sort people into risk groups. Newer US guidelines use letter categories, but the idea is the same: lower risk, middle risk, and high risk.

The risk level helps your care team decide where you should be treated. It also shows whether you need a clot-busting treatment.

Calf DVT

A clot in a small vein below the knee. Some are treated with blood thinners. Others may be watched with a repeat ultrasound in about a week to see if they grow.

Proximal DVT

A clot in the knee, thigh, or pelvis. It is more likely to travel to the lungs and is treated with a blood thinner.

Low-risk PE

Normal blood pressure, no strain on the heart, and normal heart blood tests. Many people can be treated at home with blood thinner pills.

Intermediate-risk PE

Blood pressure is normal, but the heart shows strain on ultrasound or blood tests. You are usually watched in the hospital. Most people do well with blood thinners alone.

High-risk PE

The clot causes low blood pressure or shock. This is an emergency. Treatment may include clot-busting medicine or a procedure to remove the clot.

Limb-threatening DVT

Rarely, a very large leg clot blocks so much blood flow that the leg turns blue and very painful. This needs emergency treatment.

Lab tests to know

Some people have inherited or acquired conditions that make blood clot more easily. These are called thrombophilias.

Testing is often not helpful after a provoked clot, or in people with active cancer, because the results rarely change treatment. Timing also matters. Some tests are thrown off by a new clot or by blood thinners, so your care team may wait to test.

Ask your care team whether testing makes sense for you and what the results would change.

Factor V Leiden

The most common inherited clotting gene change in people of European background. Having one copy raises clot risk a few times over. Two copies raise it more. It can be checked with a gene test, which is not affected by blood thinners.

Prothrombin gene change (G20210A)

The second most common inherited change. It makes the body produce a little more of a clotting protein. It is checked with a gene test.

Protein C and protein S

Natural proteins that keep clotting in check. Low levels raise clot risk. Levels can be falsely low during a new clot, pregnancy, estrogen use, liver disease, or warfarin, so testing is usually done later.

Antithrombin

Another natural blood thinner made by the body. An inherited low level is rare but carries a high clot risk. Heparin and a new clot can lower the level, so timing matters.

Antiphospholipid antibodies

Antibodies that can cause clots and pregnancy problems. This condition is called antiphospholipid syndrome (APS). People with APS, especially with all three antibody tests positive, usually take warfarin instead of newer blood thinner pills.

JAK2 and PNH tests

For clots in the belly or other unusual places, doctors may test for blood disorders such as an MPN (checked with JAK2) or PNH. These can cause clots even with normal blood counts.

INR

A blood test that measures how well warfarin is working. Most people on warfarin aim for an INR between 2 and 3.

D-dimer after treatment

After an unprovoked clot, your care team may check D-dimer a few weeks after you stop a blood thinner. A high result can mean a higher chance of another clot.

Main treatments

Blood thinner pills (DOACs)

Apixaban (Eliquis), rivaroxaban (Xarelto), edoxaban (Savaysa), and dabigatran (Pradaxa) are the first choice for most people. They do not need regular blood tests and have few food interactions. Apixaban and rivaroxaban can be started right away as pills. Edoxaban and dabigatran start after a few days of shots.

Low molecular weight heparin shots

Enoxaparin (Lovenox) and dalteparin are shots under the skin. They are the preferred choice during pregnancy. They may also be chosen for some cancers, such as stomach or bowel cancers with a higher bleeding risk.

Warfarin

An older blood thinner pill. It needs regular INR blood tests and steady amounts of vitamin K in your diet. It is still the best choice for some people, such as those with antiphospholipid syndrome or a mechanical heart valve.

Heparin through an IV

Often used in the hospital, especially if a procedure may be needed. Its effect wears off quickly when it is stopped.

Clot-busting medicine and procedures

Some clots are very dangerous, such as a high-risk PE or a limb-threatening DVT. For these, doctors may use clot-dissolving medicine. They may also use a catheter (thin tube) to break up or remove the clot. These raise the risk of bleeding, so they are saved for serious cases.

IVC filter

A small metal device placed in the large vein in the belly to catch clots before they reach the lungs. It is used only when you cannot take a blood thinner, or clots keep forming despite one. It should be removed when no longer needed.

How long treatment lasts

Most people take a blood thinner for at least 3 months. After a provoked clot, treatment often stops then. After an unprovoked clot, a cancer-related clot, or a repeat clot, longer or lifelong treatment is often suggested. Your care team will weigh your clot risk against your bleeding risk.

Lower-dose long-term treatment

After the first 6 months, some people can switch to a lower dose of apixaban or rivaroxaban. This still protects against new clots, with a similar or lower risk of bleeding.

Clots and cancer

For most people with cancer, apixaban, edoxaban, or rivaroxaban work about as well as heparin shots. Shots may be better for some stomach, bowel, or bladder cancers, very low platelets, or when cancer drugs interact with the pills. Some people at high risk may get a blood thinner to prevent a first clot during chemotherapy.

Treatment side effects and what helps

Minor bleeding

Easy bruising, bleeding gums, and nosebleeds are common. Use a soft toothbrush and an electric razor. Press firmly on small cuts for 10 minutes. Tell your care team if it happens often.

Serious bleeding

Rarely, blood thinners cause serious bleeding in the stomach, bowel, or brain. Signs include black or bloody stools, vomiting blood, a severe headache, or feeling faint. Get help right away. There are treatments that can reverse blood thinners in an emergency.

Heavy periods

Blood thinners can make menstrual bleeding heavier. Tell your care team. There are hormone and non-hormone options that can help, and some blood thinners may cause less bleeding than others.

Falls and head injuries

If you hit your head while on a blood thinner, get checked, even if you feel fine. Remove tripping hazards at home and wear good shoes.

Medicine and supplement interactions

Pain relievers like ibuprofen, naproxen, and aspirin raise bleeding risk. Some antibiotics, seizure medicines, antifungals, and St. John's wort can change how blood thinners work. Always ask your care team or pharmacist before starting something new.

Warfarin and food

Vitamin K in green leafy vegetables affects warfarin. You do not need to avoid these foods. Just eat about the same amount each week. Alcohol and many medicines can also change your INR.

Procedures and surgery

Tell every doctor and dentist that you take a blood thinner. For many small procedures, you can keep taking it. For larger ones, your care team will tell you when to stop and restart. Do not stop on your own.

Low platelets from heparin (HIT)

Rarely, heparin causes an immune reaction that lowers platelets and causes new clots. It usually shows up 5 to 10 days after starting heparin. If you have had HIT, tell every doctor and avoid heparin in the future.

Leg swelling after a DVT

Some people have long-term leg swelling, aching, or skin changes after a DVT. This is called post-thrombotic syndrome. Raising the leg, walking, and compression stockings may ease symptoms.

Living with and after a blood clot

Most people go back to normal activities soon after starting a blood thinner. Walking is safe and helps. Leg pain and swelling usually improve over weeks. Shortness of breath after a PE can take weeks to months to get better.

Take your blood thinner exactly as prescribed. Missing doses, especially in the first weeks, raises the risk of a new clot. Use a pill box or phone reminder. Do not stop your blood thinner without talking to your care team.

Lower your future risk. Stay active, keep a healthy weight, and do not smoke. On long trips, get up and walk every hour or two, flex your ankles, and drink water. Tell your care team before surgery or a long hospital stay, because you may need a blood thinner to prevent clots.

Estrogen in birth control pills, patches, rings, and hormone therapy raises clot risk. Talk with your care team about safer birth control options. If you want to become pregnant, plan ahead. Most blood thinner pills are not safe in pregnancy, so heparin shots are used.

If you had a clotting disorder test, ask whether your relatives should know. Testing family members is often not needed, but knowing the family history can help them before surgery or pregnancy.

A clot can be scary, and many people worry about another one. It is normal to feel anxious. Talk with your care team, and ask about support from groups such as the National Blood Clot Alliance.