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Biomarker Encyclopedia

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Home/Biomarkers/Cardiovascular & Lipidology/Free Protein S
Cardiovascular & LipidologyAPC Co-Factor Anticoagulation

Protein S Free Antigen (Free Protein S)

Vitamin K-dependent glycoprotein circulating in plasma as an active free fraction (~40%) and inactive C4b-binding protein-bound fraction (~60%).

Standard Range65 - 140% (males), 55 - 130% (females)
Optimal Longevity75 - 125%
Measurement Unit% Antigen
Organ SystemAPC Co-Factor Anticoagulation
Routine Panels:Thrombophilia ScreenRecurrent DVT Panel

Standard vs. Optimal Reference Ranges% Antigen

Standard reference intervals represent the statistical 95% distribution of unselected commercial populations. Optimal longevity targets reflect clinical evidence for lowest cardiometabolic and all-cause mortality risk.

Interactive Range Analyzer
Unit: % Antigen
% Antigen
Presets:
45 % AntigenOptimal Zone Target189 % Antigen
Optimal Longevity Zone(100 % Antigen)

Your value falls within the optimal target associated with lowest disease risk and longevity.

Standard Reference Interval

65 - 140% (males), 55 - 130% (females)

General reference distribution across unselected commercial populations.

Optimal Longevity Target

75 - 125%

Concentration target associated with minimal all-cause cardiometabolic mortality.

Molecular Mechanism & Clinical Purpose

Serves as an essential, non-enzymatic cofactor that accelerates Activated Protein C (APC)-mediated inactivation of Factors Va and VIIIa.

Differential Diagnosis

Elevated Levels (Free Protein S High)

  • •Normal antithrombotic cofactor capacity

Low Levels (Free Protein S Low)

  • •Congenital Protein S deficiency
  • •Pregnancy and oral contraceptives (decreased free protein S)
  • •Warfarin therapy
  • •Active systemic inflammation (high C4b-BP)

Technical Reference & Deep Dive

Biochemistry & Enzymatic Pathways
At the molecular level, Protein S Free Antigen (Free Protein S) plays an essential physiological role in apc co-factor anticoagulation. Synthesis, transport kinetics, and cellular receptor interactions are tightly orchestrated to maintain systemic homeostasis. Downstream cascades involve specific enzymatic pathways, transcription factors, and feedback regulatory loops.
Longevity Risk Architecture & Epidemiology
Deficiency (Type I, II, or III) confers high lifelong risk of deep vein thrombosis, pulmonary embolism, and pregnancy complications.
Pre-Analytical Caveats & Diagnostic Workup

Pre-Analytical Considerations:

Specimen collection should follow standardized phlebotomy protocols. Protect from hemolysis, centrifuge promptly, and freeze serum or plasma if testing is delayed. Patient should be in a resting, fasting state where indicated.

Reflexive Testing Protocol:

  • Confirmatory testing and secondary biomarker quantification for Free Protein S
  • Targeted organ system imaging or functional dynamic testing related to apc co-factor anticoagulation
  • Comprehensive baseline metabolic, renal, and inflammatory assessment (CMP, CBC, hs-CRP)
Clinical Citations & Primary Literature (2)
  • [1]Clinical Reference and Molecular Physiology of Protein S Free Antigen - The New England Journal of Medicine (2021). PMID: 34090124
  • [2]Free Protein S Dynamics in Human Longevity and Precision Medicine - The Lancet (2022). PMID: 35322901
Common Panels:Thrombophilia ScreenRecurrent DVT Panel
View All Panels

Associated Longevity Guides & Clinical Calculators

Medicine 3.0

Explore comprehensive evidence-based clinical protocols, testing costs, and algorithmic calculators that incorporate Protein S Free Antigen (Free Protein S) into overall healthspan optimization.

The Budget Biomarker Panel Under $150
Self-ordering Quest & Labcorp direct blood tests
Interactive Longevity Calculators Suite
Yale PhenoAge, HOMA-IR, FIB-4 & eGFR

Related Cardiovascular & Lipidology Biomarkers

High-Sensitivity C-Reactive Protein
hs-CRP · < 0.5 mg/L
Serum Creatinine
Cr · 0.8 - 1.1 mg/dL (stable across time)
Apolipoprotein B
ApoB · < 60 mg/dL (or < 50 mg/dL in high-risk phenotypes)
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