What is Free Protein S?
There are two types of Protein S – free and complex. Free Protein S is ready and available to bind to Protein C. Both proteins play an important part in coagulation or clotting. If free Protein S level is too low, there is not enough of the protein to bind with Protein C and irregular clotting occurs – particularly the formation of clots and reduced or restricted blood flow.
The free Protein S test will not be ordered as a standalone test. The test will be ordered as part of a series of blood tests to determine the cause and effect of a clotting event or to help diagnose disease or illness. Pregnant women experiencing symptoms of preeclampsia may have free Protein S levels tested to support the preeclampsia diagnosis.
Normal Value Range
- Negative Pregnancy Adult: 70 to 140 percent
- Pregnancy Trimester One: 34 to 133 percent
- Pregnancy Trimester Two: 19* to 113 percent
- Pregnancy Trimester Three: 20* to 65 percent
Low free Protein S percentages are indicative of a clotting disorder, autoimmune disease or preeclampsia. Protein levels are also affected by liver and kidney disease – though other tests are required to diagnose these conditions.