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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 does not usually cause any medical problems. 

Protein C deficiency is an inherited condition. It can cause mild or severe symptoms, depending on whether you inherit one or two abnormal copies of the gene. About 1 in 500 people has a mild protein C deficiency, and about 1 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 may need 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?

Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you. 

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 is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be 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.   

Online Medical Reviewer: Freeborn, Donna, PhD, CNM, FNP
Online Medical Reviewer: Haldeman-Englert, Chad, MD
Date Last Reviewed: 11/1/2017
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