Fibrinogen Testing: Clotting Factor That Predicts More Than Clots
Content last reviewed 2026-09-12 · Educational information — not medical advice
Quick answer
Fibrinogen, clotting factor I, converts to fibrin to form clot mesh — but also acts as an acute-phase reactant rising with inflammation. High levels predict cardiovascular risk modestly; low levels raise bleeding concerns in liver failure or consumptive coagulopathy.
Fibrinogen's dual personality
Clotting: thrombin cleaves fibrinogen→fibrin monomers that polymerize into the structural mesh stabilizing platelet plugs. Inflammation: fibrinogen production surges with IL-6 (like CRP), making it a cardiovascular-risk marker — though CRP does this job more cleanly clinically.
Who should test
- Unexplained bleeding workup: isolated low fibrinogen suggests rare congenital deficiency (dysfibrinogenemia) or consumption (DIC)
- Liver disease: low fibrinogen tracks synthetic failure (half-life ~4 days — acute changes)
- Cardiovascular risk refinement: elevated fibrinogen modestly adds information — rarely ordered alone for this
- DIC monitoring: falling fibrinogen alongside rising D-dimer tracks consumptive coagulopathy
Reference ranges
Typical 200–400 mg/dL. Levels >700 acute-phase, often post-operative or infectious. Below 150 in liver disease raises bleeding concern; below 100 associated with spontaneous bleeding risk in surgical contexts (trigger for cryoprecipitate replacement).
Pregnancy note
Fibrinogen rises 50-100% during normal pregnancy — a physiological hypercoagulable adaptation. Expected high values in third trimester represent health, not disease.
Order this test online
Direct-access laboratory testing — no appointment or doctor visit required. Results delivered as secure PDFs.
We may earn a commission when you order through partner links. Educational content only — never a substitute for professional medical advice.
Related guides
Frequently asked questions
Can exercise raise fibrinogen?
Moderate exercise LOWERs fibrinogen chronically; acute exhaustive exercise transiently elevates it as acute-phase response.
Does fish oil affect fibrinogen?
Omega-3 supplements show modest fibrinogen-lowering effects — not clinically meaningful for dosing decisions.