Protein S Assay
- Sample Type
- Plasma
- Fasting
- No
- Unit
- %
Function
Protein S is a Vitamin K-dependent plasma glycoprotein that serves as a critical cofactor for Activated Protein C (APC). Together, they inactivate factors Va and VIIIa in the coagulation cascade, thereby acting as a natural anticoagulant. Without sufficient Protein S, the body is unable to effectively 'turn off' the clotting process, leading to a prothrombotic state.
Why it is Ordered
This assay is used to investigate hypercoagulable states (thrombophilia). It is typically ordered for:
- Unexplained Blood Clots: Patients who experience Deep Vein Thrombosis (DVT) or Pulmonary Embolism (PE), especially at a young age.
- Family History: Individuals with a strong family history of clotting disorders.
- Recurrent Miscarriage: As some clotting disorders are linked to pregnancy complications.
Associated Conditions
- Protein S Deficiency: Can be hereditary (genetic mutations) or acquired.
- Liver Disease: Since Protein S is produced in the liver.
- Vitamin K Deficiency: Necessary for the synthesis of functional Protein S.
- Disseminated Intravascular Coagulation (DIC): Where clotting factors are consumed rapidly.
Check Your Result
Check Your Result
Enter your lab result to see where you stand compared to the standard reference range.
Why Context Matters
Protein S testing is highly sensitive to the patient's current medication and physiological state. Testing should never be performed during an acute clotting event or while the patient is on Warfarin (Coumadin), as both will naturally deplete Protein S levels and yield a false-positive deficiency result. Pregnancy and oral contraceptive use also naturally lower Protein S levels. A second opinion is vital to ensure the test is timed correctly (usually 4-6 weeks after stopping anticoagulants).
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
Clinical References
Source-of-truth databases and clinical guidelines for Protein S Assay:
Official Sources
- Protein C and Protein S - Testing.comTesting.com
Research & Guidelines
- PubMed: Protein S Assay Clinical GuidelinesNCBI / PubMed
Related Indicators
Medically Reviewed by Dr. Binoy Babu, MBBS
Board Certified Doctor • 10+ Years Clinical Experience
Dr. Babu is a practicing physician dedicated to empowering patients with clear, actionable medical information. He founded 2opi to bridge the gap between complex lab reports and patient understanding, ensuring everyone has access to a reliable second opinion.
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