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If You Have a Blood Clot

This information describes what a blood clot is and how it is treated.

If you cut yourself, you want your blood to clot so that the bleeding stops. However, your blood can also clot without having an injury. Patients with cancer have a higher risk of developing unwanted blood clots.

Types of Blood Clots

There are two types of blood clots that can be dangerous.

Deep vein thrombosis (DVT) is a blood clot deep in the vein of an arm or leg. It is occasionally found in other parts of the body, but this is rare. The clot blocks normal blood flow to the vein. When DVT occurs in an arm or leg, it causes swelling, redness, and pain in the area. If left untreated, new clots can form. This can make the swelling and pain worse, and lead to difficulty walking, an infection, or skin ulcers.

Pulmonary embolism (PE) is a blood clot in an artery of the lung. Most of the time, it happens when DVT in the leg travels up to the lungs. Once there, it can block the blood flow to an artery, which can cause the oxygen levels in the blood to drop. This can cause shortness of breath, chest pain, and severe breathing problems. PE can cause death if it is not treated quickly.

Treatment of Blood Clots

Anticoagulants, or blood thinners, are medications that thin your blood. They are the most common treatment for blood clots. They help do two things:

  • Prevent your body from forming new clots
  • Allow your body's own system of breaking up clots to work

Blood thinners can be given:

  • By injection into a vein or under the skin
  • By mouth as a tablet

Your doctor will decide which form is best for you and how long you will need to take it. Most patients stay on blood thinners for at least 3 months. Some may stay on them for the rest of their lives. If you have been treated for a blood clot in the past, or if you are also having chemotherapy, you may need to stay on them longer.


Most blood clots are treated with heparin, which is the most commonly used blood thinner. If you are admitted to the hospital for treatment of your blood clot, you may receive heparin by injection into your vein.

Low molecular weight heparin is also used to treat blood clots. It is injected under your skin and can be given in the hospital or at home. Sometimes, it is used for a short time alone or in combination with a tablet form of blood thinner. When the right level of the tablet form is reached in your blood, you will no longer need the injections. This usually takes at least 5 days.

Examples of low molecular weight heparins are:

  • Dalteparin (Fragmin®)
  • Tinzaparin (Innohep®)
  • Enoxaparin sodium (Lovenox®)

Your nurse will teach you and a caregiver how to give the injections. This may feel scary at first, but most patients and caregivers become comfortable doing it.

If you get the medication here at Memorial Sloan Kettering Cancer Center, the syringe will have a very short needle and will already be filled with the medication. You will be given written information that explains all the steps to giving the injection and you will practice while your nurse watches.

If you get the medication from an outside pharmacy, you may have different instructions. Ask your pharmacist how the medication is supplied. If it comes in a vial, you will need to learn how to draw it up into a syringe. Call your nurse for instructions.


The tablet form of blood thinner is called warfarin (Coumadin®). It takes several days for it to build up in your body to prevent blood clotting. While this is happening, you will also use the injectable form, which works more quickly to thin your blood. Once your blood is thin enough, you will no longer need to take the injections. You will keep taking warfarin.

While you are on warfarin, you will need to have an INR blood test done. This test measures how long it takes your blood to clot. When you first start taking warfarin, you may need to have the test done every week or more often. The test will be done less often as your blood levels become stable. Your doctor may change your daily dose of warfarin based on the results of your INR. This is to make sure your blood is thin enough to prevent clots, but not too thin. If your blood is too thin, you may bleed too much if injured.

Important Instructions

  • While you are taking blood thinners, do not take the following:
    • Aspirin or products containing aspirin (e.g., Bufferin®, Anacin®)
    • Nonsteroidal anti-inflammatory drugs (NSAIDs; e.g., ibuprofen, Motrin®, Aleve®)
    • Vitamin E

They can cause bleeding problems. Instead, take acetaminophen (Tylenol®) for any pain or discomfort.

  • Tell your doctor or nurse if you are taking any other medications or have changed medications. Some may change the way your blood thinner works. These include:
    • Medications that do and do not require a prescription
    • Herbal remedies
    • Vitamins
    • Dietary supplements

Tell your other doctors and dentist that you are taking a blood thinner.

Call Your Doctor or Nurse if You Have:

  • Increased pain, swelling, or both in your affected arm or leg
  • New pain, swelling, or both in your other arm or leg
  • Shortness of breath
  • Severe or ongoing headaches
  • Nose bleeds
  • Bleeding gums
  • Blood in your urine, stool, vomit, or in the mucus that you cough up through your mouth
  • A heavier menstrual flow than usual
  • Bleeding that does not stop
  • Bruising that does not go away
  • Fallen or hurt yourself in any way
  • Plans for any dental procedure or surgery
  • Stopped taking your blood thinner for any reason
  • Any unexpected, unexplained side effects
  • Any questions or concerns