Protein C Activity

Normally, proteins C and S work together to prevent your blood from clotting too much.

However, if you have a protein C or S deficiency (when your body doesn't make enough of these proteins), your blood may clot too much. It may also clot even when you don't have an injury. Low protein C is linked to clots forming in your veins (venous thrombosis).

A protein C deficiency can be inherited or acquired. Acquired causes include taking blood thinners that block vitamin K (such as warfarin), vitamin K deficiency, liver disease, cancer, severe clotting disorders that use up clotting factors (such as disseminated intravascular coagulation), recent surgery, major trauma, and immaturity of the liver in newborns.

Some blood-thinning medicines can also affect the test result. Vitamin K antagonists like warfarin lower measured protein C activity, while heparins and direct oral anticoagulants (such as dabigatran, argatroban, rivaroxaban, apixaban, and edoxaban) can falsely raise the result, so let your provider know about any medicines you are taking.

Higher than normal levels of protein C or S are not known to cause any health problems.

Lower than normal levels of protein C or S, or proteins that aren't working well, mean that you have a higher risk of developing a blood clot. Your level of risk depends on how abnormal your test results are.

If your provider thinks your protein C or S deficiency is inherited, you may need a genetic test to find out for sure. Having an inherited deficiency doesn't mean that you'll develop a blood clot. But it does mean that your risk for developing a clot will be increased for the rest of your life.

If your protein C or S deficiency is acquired, the deficiency may be temporary or long-lasting. In certain cases, acquired deficiencies may get worse over time. Acquired deficiency can be caused by conditions such as liver disease, cancer, vitamin K deficiency, or recent surgery or trauma, and certain blood-thinning medicines (such as warfarin) can also lower your result.