What is blood clots (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.

When should I call my care team?

New or worse swelling, pain, warmth, or redness in one leg or arm; Sudden shortness of breath, or trouble breathing; Chest pain, especially when you breathe in deeply; Coughing up blood; A racing heartbeat, fainting, or feeling like you might pass out; Bleeding that will not stop after 10 minutes of pressure; Black, tarry, or bloody stools, red or brown urine, or vomiting blood or what looks like coffee grounds; A fall or hit to the head while on a blood thinner, even if you feel fine; A sudden, severe headache, weakness on one side, or trouble speaking; If it feels very bad, call 911.

Blood clots (DVT and PE)

Blood clots in the veins are common and serious, but they are very treatable, and most people recover well with blood thinners and good follow-up.

Hi, I'm Rosa. Today we'll go through blood clots together, one step at a time. I'll keep it simple, and you can pause me, go back, or skip ahead whenever you like. Just so you know, this is for learning only. It is not medical advice, so please check everything with your own doctor and care team. Okay, let's get started.

What a blood clot is

Let's start with the basics. Blood is meant to clot when you are cut. Sometimes a clot forms inside a vein when it should not. A clot in a deep leg vein is called deep vein thrombosis. It can cause swelling, pain, or redness in one leg. Sometimes a piece breaks off and travels to the lungs. That is called a pulmonary embolism. It needs care right away. Blood clots are common, and they are not cancer. With treatment, most clots stop growing. Your body slowly breaks them down.

Types of clots

Let's talk briefly about the types. Deep vein thrombosis is a clot in a deep leg vein. Pulmonary embolism is a clot that has traveled to the lungs. A provoked clot has a clear trigger, like surgery or a hospital stay. An unprovoked clot has no clear trigger. Cancer and some cancer treatments can also make clots more likely. Clots can also form in the arm, often near a long-term line. Some clots form in unusual places, like the belly. A clot that comes back is called a recurrent clot.

Tests you may have

Now let's talk about tests. A blood test called D-dimer looks for pieces of broken-down clot. A normal result can help rule out a clot. A leg ultrasound uses sound waves to see the veins. It is the main test for a leg clot. A special CT scan with dye shows the blood vessels in the lungs. A lung scan can be used if dye is not a good choice. Heart tests show if a lung clot strains the heart. Blood tests help pick the safest blood thinner.

How serious it is

Next up, let's talk about how serious a clot is. Doctors look at where the clot is and how big it is. They also look at your heart and breathing. Why does this matter? It helps your team decide where you should be treated. It also helps everyone talk the same language. A small clot below the knee may be watched with another ultrasound. A clot higher in the leg is treated with a blood thinner. Many people with a lower-risk lung clot are treated at home. A high-risk lung clot is an emergency.

Lab tests to know

Before we move to treatment, there are some things to know. Some people have conditions that make blood clot more easily. Some are passed down in families. There are different lab tests for these. Each one has a different role. Many people do not need them at all. Timing matters too. A new clot or a blood thinner can change some results. Your doctor will tell you if testing makes sense for you. They will explain what the results mean. You can read more in the guide. The Questions to ask page can help too.

Main treatment options

Now let's look at treatment. Blood thinners are the main treatment. They keep the clot from growing and stop new clots. Blood thinner pills are the first choice for most people. Some people use shots under the skin, like during pregnancy. An older blood thinner pill needs regular blood tests. Very dangerous clots may need clot-busting medicine or a procedure. A small filter in a large vein is used only in rare cases. Most people take a blood thinner for at least three months. Clinical trials are research studies that may offer new options. Ask your care team.

Side effects and what helps

Let's talk about side effects. The main side effect of blood thinners is bleeding. Easy bruising and nosebleeds are common. Use a soft toothbrush and an electric razor. Press firmly on small cuts for ten minutes. Rarely, serious bleeding can happen. If you hit your head, get checked, even if you feel fine. Some pain relievers and supplements raise bleeding risk. Ask before starting anything new. Tell every doctor and dentist that you take a blood thinner. We have a whole side effects guide on this site.

Living well after a clot

Last, let's talk about living well. Most people go back to normal activities soon. Walking is safe and helps. Take your blood thinner exactly as prescribed. Never stop it without talking to your care team. On long trips, get up and walk every hour or two. It is normal to worry about another clot. Support groups can help. Call right away for trouble breathing, chest pain, or a newly swollen leg. If it feels very bad, call 911. Also see our new Screening, prevention and survivorship section.

You did great today. That was a lot, and you took it one step at a time. Write down your questions and bring them to your next visit. Call your care team any time something worries you. You are not alone in this.

Call your care team right away if you have

New or worse swelling, pain, warmth, or redness in one leg or arm
Sudden shortness of breath, or trouble breathing
Chest pain, especially when you breathe in deeply
Coughing up blood
A racing heartbeat, fainting, or feeling like you might pass out
Bleeding that will not stop after 10 minutes of pressure
Black, tarry, or bloody stools, red or brown urine, or vomiting blood or what looks like coffee grounds
A fall or hit to the head while on a blood thinner, even if you feel fine
A sudden, severe headache, weakness on one side, or trouble speaking
If it feels very bad, call 911.

Side effects: what helps

Sources

Quick answers

What is blood clots (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.
When should I call my care team?: New or worse swelling, pain, warmth, or redness in one leg or arm; Sudden shortness of breath, or trouble breathing; Chest pain, especially when you breathe in deeply; Coughing up blood; A racing heartbeat, fainting, or feeling like you might pass out; Bleeding that will not stop after 10 minutes of pressure; Black, tarry, or bloody stools, red or brown urine, or vomiting blood or what looks like coffee grounds; A fall or hit to the head while on a blood thinner, even if you feel fine; A sudden, severe headache, weakness on one side, or trouble speaking; If it feels very bad, call 911.

Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.