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Blood clot facts and treatment


Blood clot facts

What is an artery?
An artery is a blood vessel. Arteries carry blood from the heart to everywhere else in the body. The blood that flows through arteries has lots of oxygen in it. The beating of your heart is what moves the blood through your arteries.

What is a vein?
A vein is also a blood vessel. Veins carry blood back to the heart from the rest of the body. Blood in the veins is pushed back to the heart by your muscles squeezing together. The blood moves through valves that act like a gate and will not let the blood flow backwards. Blood in the veins has less oxygen than the blood in the arteries.

What is a blood clot?
A blood clot is blood that becomes a solid instead of a liquid.

Why does blood clot?
Clotting is normally a good thing. Clots are your body’s way of protecting you from bleeding too much. If you cut yourself or bump into something your body releases clotting factors (proteins) that travel to where the injury occurred. The clotting factors work with your platelets to form a clot and stop the bleeding. It is like putting a bandage on from the inside. What you will see is a scab or a bruise.

What is a thrombus?
A thrombus is a blood clot that forms in a blood vessel and stays there. This can happen by chance or sometimes it happens if you have a bad infection or a specific illness or as a side effect of having an IV with a larger catheter. When it happens you get a clot that is bigger than normal and not in the right place.

Sometimes you may get a clot without an illness or infection. This is known as a spontaneous blood clot or spontaneous thrombus.

What is an embolus?
An embolus is a small piece of a thrombus (clot) that breaks away and moves through the blood vessel, usually to the lungs or brain. An embolus is a life-threatening event but if it is going to happen it will happen in the first few days or weeks after the clot forms.

Where does a thrombus form?
A thrombus can be in an artery or a vein. Veins and arteries are like one-way streets and when a blood clot forms it can make a roadblock. In a sense, the blood behind the clot gets caught in a traffic jam.

What happens if I have a thrombus in an artery?
If you have a blood clot in one of your arteries, it does not let the blood, which carries oxygen, get to the muscle or tissue beyond the clot. The clot acts like a barricade and will not let the blood get through. When this happens the tissue beyond the clot can become damaged. Your tissue and muscles need oxygen to work correctly and to stay healthy.

What happens if I have a thrombus in a vein?
A deep vein thrombosis (thrahm-BOW-sis) is a blood clot in a large vein that is deep inside a muscle, usually in the legs. If you have a clot in a deep vein, it can prevent the blood from getting back to your heart. The blood gets trapped behind the clot and can make the area behind the clot swell and hurt. A clot can damage the valves (gates) around it. If this happens the blood will flow backwards, which can cause more pain and swelling and may lead to post thrombotic syndrome (thrahm-BAH-tik SIN-drohm).

deep vein thrombosis

What is post thrombotic syndrome?
Post thrombotic syndrome (PTS) happens when the blood vessels are clogged and valves are damaged from the clot. Because of this the valves (gates) do not close completely and blood flows backwards. If this happens, the area (such as a leg) will swell and could be painful because the blood gets stuck or pools. In the severe form, PTS can cause ulcers (sores) to form on the skin that are hard to heal.

How can PTS be prevented?
PTS can be prevented or minimized by following these steps:

  • Treat the thrombus with medicine during the first few months.
  • Wear compression stockings (long socks that feel tight on the legs).
  • Elevate the leg or arm above your heart for 20 to 30 minutes every day. It is best to do this in the middle of the day.

Why does the thrombus have to be treated?
If you have a blood clot, you will need to be on medicine to keep the clot from getting bigger or coming back if it is gone. The medicine also will help make the clot smaller. The treatment will help prevent PTS by keeping the remaining thrombus as small as possible.

Will I get another thrombus?
Your doctor will look at your medical history and family history, take a blood sample, and run a series of tests to see if you are at a higher risk for more blood clots. You have a greater chance of getting another thrombus within a few days to several months of the first thrombus, but it still can happen later. Treating the clot with medicine helps prevent it from coming back.

Blood clot treatment

If you have a blood clot, the doctor may prescribe a medicine to help prevent the clot from getting bigger or coming back if it is gone.

When your blood clot is first found, your doctor may give you medicine that can break down the clot. This medicine is known as a thrombolytic (thrahm-BOW-lih-tik). Your doctor will ask you questions to find out if you are able to receive this medicine. This usually happens when the blood clot is first discovered.

Another medicine used for blood clots is low molecular weight heparin called enoxaparin (Lovenox®). Enoxaparin is given as a shot under the skin with a very small needle. This medicine helps keep the clot from getting any bigger. Sometimes, it can help your body shrink the blood clot. To make sure you receive the right amount of medicine, you will need to have your blood tested every month. This lets your doctor know if you

have enough medicine in your body to work on the clot and prevent any more from forming. You must have blood samples taken when your doctor asks you to do so. If you have too much medicine in your body, you may bleed more than normal. If you do not have enough medicine in your body you could get another clot.

Follow-up testing
After you have been treated for a clot for about 3 months, the doctors will want to see if it is bigger, smaller, or the same size. They do this with an ultrasound test. Ultrasound lets the doctors see a picture of the clot. Whatever size your clot is at this time is probably the size it will stay. However, you still need to take your medicine to make sure you do not get another clot.

The longer you have the clot the more attached it gets to the blood vessel wall. After 2–4 weeks it is unlikely that the clot will “break off” and move to another part of the body.

Another medicine
After taking enoxaparin for 3–6 months, your doctor will decide if you are ready to stop taking this medicine. You may be able to stop the medicine or you may be switched to another drug that you would take by mouth. This medicine is called warfarin (Coumadin®). If the doctor prescribes warfarin, you will need to take both your enoxaparin and the warfarin for at least 5 days. At that time, your doctor will do a blood test to make sure the warfarin is working before taking you off the enoxaparin. Do not stop the enoxaparin too early because you will have a much greater chance of having a new clot at that time.

The length of treatment and whether you continue on medicine for the long term will depend on why you developed the clot in the first place. Your doctor will discuss this plan with you.


If you have further questions about blood clots or their treatment, talk to your doctor or nurse.

Helpful websites

National Blood Clot Alliance

National Hemophilia Foundation


This document is not intended to take the place of the care and attention of your personal physician or other professional medical services. Our aim is to promote active participation in your care and treatment by providing information and education. Questions about individual health concerns or specific treatment options should be discussed with your physician.

St. Jude complies with health care-related federal civil rights laws and does not discriminate on the basis of race, color, national origin, age, disability, or sex.

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