Understanding Lab Tests for Protein S Deficiency
Written by Private MD Labs Medical Writing Team • Last Updated: September 8, 2025
Protein S deficiency is a blood clotting disorder that increases the risk of developing abnormal blood clots, particularly deep vein thrombosis and pulmonary embolism. This condition occurs when the body doesn't produce enough protein S, a natural anticoagulant protein that helps prevent excessive clotting.
Recommended Test
Protein S Antigen, Free
This is the primary diagnostic test for protein S deficiency. It measures the amount of free protein S antigen in the blood, which is the active form of the protein. Low levels of free protein S antigen indicate a deficiency, confirming the diagnosis of this clotting disorder.
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Diagnosing Protein S Deficiency
Protein S deficiency can be either inherited (genetic) or acquired due to certain medical conditions or medications. Since symptoms may not appear until a clotting event occurs, laboratory testing is essential for diagnosis, especially in individuals with a family history of clotting disorders or unexplained blood clots.
When Testing May Be Recommended
Healthcare providers may recommend protein S testing for individuals with unexplained blood clots, recurrent clotting episodes, a family history of clotting disorders, or clots occurring at a young age. Testing may also be considered before starting certain medications or surgical procedures in high-risk individuals.
Important Considerations
The information here is for educational purposes only and is not a substitute for professional medical advice. Always consult with a healthcare provider for diagnosis and treatment.
