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Protein C (Blood)

Does this test have other names?


What is this test?

This test measures the level of protein C in your blood. Protein C helps your blood clot normally.

If you have too little protein C (protein C deficiency), it means that your blood may clot too much. Problems with blood clotting can be quite serious and possibly fatal if a blood clot reaches the lungs (pulmonary embolism).

Having too much protein C may not let your blood clot well. You may be at risk for bleeding.

Protein C deficiency is an inherited condition. It can cause mild or severe symptoms, depending on whether  you inherit one or two abnormal genes. About one in 500 people has a mild protein C deficiency, and about one in 4 million babies is born with a severe protein C deficiency. Protein C deficiency may very rarely be acquired through various causes.

Even people with mild protein C deficiency are at risk for serious blood clots that can be caused by:

  • Being pregnant

  • Having surgery

  • Getting older

  • Not moving around often

Why do I need this test?

You might have this test if you:

  • Had a blood clot in the past

  • Have a family member with a protein C deficiency

  • Have a family member with a blood clotting disorder

  • Have blood that does not clot normally

What other tests might I have along with this test?

Your healthcare provider may look for any other abnormalities in your blood that could explain your blood clotting problems.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

A normal level of protein C in the blood is between 70% and 140%. Lower-than-normal readings may mean that you have a protein C deficiency.

A lower-than-normal level of protein C may be caused by:

  • Blood-thinning medicines, such as warfarin

  • Kidney problems

  • Deficiency in vitamin K

  • Inherited protein C deficiency

  • Condition that causes the blood to clot too much (consumptive coagulopathy)

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Taking certain medicines may affect your test results. If you take a medicine called stanozol or birth control pills, you may have a higher-than-normal level of protein C in your blood.

How do I get ready for this test?

Your Healthcare provider will tell you if you need to stop taking any of your usual medicines on the day of the test. Ask your provider whether you should avoid eating or drinking anything for several hours before the test. Be sure your provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.   

Medical Reviewers:

  • Freeborn, Donna, PhD, CNM, FNP
  • Hanrahan, John, MD