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Protein C and Protein S Tests

What are protein C and protein S tests?

These tests measure the levels of protein C and protein S in your blood. Protein C and protein S tests are two separate tests that are often done at the same time.

Protein C and protein S work together to prevent your blood from clotting too much. Normally, your body makes blood clots to stop bleeding after a cut or other injury. If you don't have enough protein C (protein C deficiency) or enough protein S (protein S deficiency), your blood can clot more than you need it to. If this happens, you may get a clot that partly or completely blocks blood flow in a vein or artery. These clots can form in the arms and legs and travel to your lungs. When a blood clot forms in the lungs it's called a pulmonary embolism. This condition is life-threatening.

Protein C and protein S deficiencies can be mild or severe. Some people with mild deficiencies never have a dangerous blood clot. But certain factors can increase the risk. These include surgery, pregnancy, certain infections, and extended periods of inactivity, such as being on a long airline flight.

Protein C and protein S deficiencies are sometimes inherited (passed down from your parents), or can be acquired later in life. Testing may help find ways to prevent the formation of clots, regardless of how you got the deficiency.

Other names: protein C antigen, protein S antigen

What are they used for?

Protein C and protein S tests are used to diagnose clotting disorders. If tests show you have a protein C or a protein S deficiency, there are medicines and lifestyle changes you can make to reduce your risk of clots.

Why do I need protein C and protein S tests?

You may need these tests if you have certain risk factors. You may be at higher risk of a protein C or a protein S deficiency if you:

  • Have a family member who has been diagnosed with a clotting disorder. Protein C and protein S deficiencies can be inherited.
  • Had a blood clot that can't be explained
  • Had a blood clot in an unusual location such as the arms or the blood vessels of the brain
  • Had a blood clot and are under the age of 50
  • Had repeated miscarriages. Protein C and protein S deficiencies sometimes cause clotting problems that affect pregnancies.

What happens during protein C and protein S testing?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

Your health care provider may tell you to avoid certain medicines for several days or longer before your test. Blood thinners, medicines that prevent clots, can affect your results.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

If your results show low levels of protein C or protein S, you may be at risk of a dangerous clot. While there is no cure for protein C and protein S deficiencies, there are ways to reduce your risk of clots.

Your health care provider will make a treatment plan based on your results and health history. Your treatment may include medicines that make it harder for the blood to clot. These include blood thinning drugs called warfarin and heparin. Your provider may also recommend lifestyle changes, such as not smoking and not using birth control pills.

If you have questions about your results, talk to your health care provider.

Is there anything else I need to know about protein C and protein S tests?

If you have a family history or previous history of clotting, and are pregnant, be sure to tell your health care provider. Protein C and protein S deficiencies can cause dangerous clots during pregnancy. Your provider can recommend steps to ensure you and your baby stay healthy. These may include medicines, and/or frequent tests to monitor your condition.

References

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  2. March of Dimes [Internet]. White Plains (NY): March of Dimes; c2018. Thrombophilias [cited 2018 Jun 25]; [about 3 screens]. Available from: https://www.marchofdimes.org/complications/thrombophillias.aspx
  3. Mayo Clinic: Mayo Medical Laboratories [Internet]. Mayo Foundation for Medical Education and Research; c1995–2018. Test ID: PCAG Protein C Antigen, Plasma; Clinical and Interpretive [cited 2018 Jun 25]; [about 4 screens]. Available from: https://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/9127
  4. Mayo Clinic: Mayo Medical Laboratories [Internet]. Mayo Foundation for Medical Education and Research; c1995–2018. Test ID: PSTF Protein S Antigen, Plasma; Clinical and Interpretive [cited 2018 Jun 25]; [about 4 screens]. Available from: https://www.mayomedicallaboratories.com/test-catalog/Overview/83049
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  8. NIH U.S. National Library of Medicine: Genetics Home Reference [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Protein C deficiency; 2018 Jun 19 [cited 2018 Jun 25]; [about 3 screens]. Available from: https://ghr.nlm.nih.gov/condition/protein-c-deficiency
  9. NIH U.S. National Library of Medicine: Genetics Home Reference [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Protein S deficiency; 2018 Jun 19 [cited 2018 Jun 25]; [about 3 screens]. Available from: https://ghr.nlm.nih.gov/condition/protein-s-deficiency
  10. NORD: National Organization for Rare Disorders [Internet]. Danbury (CT): NORD: National Organization for Rare Disorders; c2018. Protein C Deficiency [cited 2018 Jun 25]; [about 3 screens]. Available from: https://rarediseases.org/rare-diseases/protein-c-deficiency
  11. UF Health: University of Florida Health [Internet]. University of Florida; c2018. Protein C blood test: Overview [updated 2018 Jun 25; cited 2018 Jun 25]; [about 2 screens]. Available from: https://ufhealth.org/protein-c-blood-test
  12. UF Health: University of Florida Health [Internet]. University of Florida; c2018. Protein S blood test: Overview [updated 2018 Jun 25; cited 2018 Jun 25]; [about 2 screens]. Available from: https://ufhealth.org/protein-s-blood-test
  13. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2018. Health Encyclopedia: Protein C (Blood) [cited 2018 Jun 25]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid;=protein_c_blood
  14. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2018. Health Encyclopedia: Protein S (Blood) [cited 2018 Jun 25]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid;=protein_s_blood
  15. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Health Information: Blood-Clotting Disorders: Topic Overview [updated 2017 Mar 20; cited 2018 Jun 25]; [about 2 screens]. Available from: https://www.uwhealth.org/health/topic/special/blood-clotting-disorders/aa106556.html
  16. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Health Information: Deep Vein Thrombosis: Topic Overview [updated 2017 Mar 20; cited 2018 Jun 25]; [about 2 screens]. Available from: https://www.uwhealth.org/health/topic/major/deep-vein-thrombosis/aa68134.html#aa68137

The medical information provided is for informational purposes only, and is not to be used as a substitute for professional medical advice, diagnosis or treatment. Please contact your health care provider with questions you may have regarding medical conditions or the interpretation of test results.

In the event of a medical emergency, call 911 immediately.