WellAlly Logo
WellAlly康心伴
Back to Biomarkers
Cardiology

Fibrinogen: The Clotting and Inflammation Marker

Fibrinogen is a clotting factor and acute phase reactant. Elevated levels increase blood viscosity, promote clot formation, and are associated with higher cardiovascular risk.

Reference: 200-400 mg/dL (varies by lab), optimal < 300 mg/dL mg/dL

Key Takeaway

Fibrinogen is like a double-edged sword—essential for clotting when you're bleeding, but dangerous when elevated chronicallyDanesh J, et al. 2005. High fibrinogen makes blood thicker and stickier, increasing the risk of clots in arteries (heart attack, stroke) and veins (DVT, PE).

What is Fibrinogen?

Fibrinogen (also called Factor I) is a protein produced by the liver that's essential for blood clotting. When you bleed, fibrinogen is converted to fibrin, which forms the structural mesh of blood clots. Fibrinogen is also an acute phase reactant—levels rise during inflammation.

Think of fibrinogen as the raw material for clot formation. Your body always needs some available for emergency repairs. But when there's too much circulating fibrinogen, blood becomes thick and prone to inappropriate clotting.

Why Fibrinogen Matters

  • Thrombosis risk: High levels increase clot formationLowe GD, et al. 2020
  • Blood viscosity: Makes blood thicker and harder to pump
  • Inflammation marker: Levels rise with inflammatory states
  • Plaque contribution: Fibrinogen deposits directly in plaques
  • Risk predictor: Independent predictor of cardiovascular eventsDanesh J, et al. 2005
  • Optimal (＜ 250 mg/dL): Lowest cardiovascular riskWilhelmsen L, et al. 2019
  • Normal (250-350 mg/dL): Typical range
  • Borderline (350-400 mg/dL): May indicate inflammation
  • High (> 400 mg/dL): Increased cardiovascular and thrombosis risk
  • Very High (> 500 mg/dL): Significant risk, requires investigation

Fibrinogen and Cardiovascular Risk

Elevated fibrinogen contributes to cardiovascular disease through multiple mechanismsDanesh J, et al. 2005:

Acute Phase Reactant

Fibrinogen rises during any inflammatory state. If you're sick, recovering from surgery, or have an infection, your fibrinogen will be elevatedAHA, 2021. Don't test during acute illness—wait until you're healthy for at least 2-3 weeks to get an accurate baseline level.

Clinical Context

Fibrinogen is particularly useful when:

  • Risk assessment: Adds independent risk information beyond traditional factorsLowe GD, et al. 2020
  • Unexplained thrombosis: Recurrent clots warrant fibrinogen testing
  • Inflammatory monitoring: Track disease activity in autoimmune conditions
  • Preventive screening: May identify high-risk individuals

The Coagulation Cascade

Fibrinogen is the final substrate in the clotting cascadeISTH, 2021:

  1. Injury activates clotting factors
  2. Thrombin is generated
  3. Thrombin converts fibrinogen → fibrin
  4. Fibrin mesh forms the clot structure
  5. Platelets get trapped in the mesh

When fibrinogen is high, there's more substrate available for clot formation—making clots form more easily.

Related Testing

  • hs-CRP: Inflammation marker (correlates with fibrinogen)
  • D-dimer: Clot breakdown product (if clot suspected)
  • Homocysteine: Also increases clotting risk

FAQ

Track Your Health Journey

Monitor your biomarkers over time to understand your health trends.

Fibrinogen: The Clotting and Inflammation Marker | Biomarker Guide