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Protein C blood test

Autoprothrombin IIA

Protein C is a normal substance in the body that prevents blood clotting. A blood test can be done to see how much of this protein you have in your blood.

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How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

Certain medicines can change blood test results.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

You may need this test if you have an unexplained blood clot, or a family history of blood clots. Protein C helps control blood clotting. A lack of this protein or problem with the function of this protein may cause blood clots to form in veins.

The test is also used to screen relatives of people who are known to have protein C deficiency. It may also be done to find the reason for repeated miscarriages.

Normal Results

Normal values are 60% to 150% inhibition.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your provider about the meaning of your specific test results.

What Abnormal Results Mean

A lack (deficiency) of protein C can lead to excess clotting. These clots tend to form in veins, not arteries.

Protein C deficiency can be passed down through families (inherited). It can also develop with other conditions, such as:

A problem such as a sudden blood clot in the lung may reduce the protein C level.

Protein C level rises with age, but this does not cause any health problems.

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

Related Information

Protein S blood test
Blood clots
Bleeding

References

Anderson JA, Hogg KE, Weitz JI. Hypercoagulable states. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 140.

Chernecky CC, Berger BJ. Protein C (autoprothrombin IIA) - blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:927-928.

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Review Date: 1/29/2019  

Reviewed By: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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