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Fibrinogen
The plasma protein that becomes fibrin, the scaffold of a clot. Rises with inflammation and clotting risk; falls in severe bleeding disorders.
Other names: Fibrinogen, Factor ISection: Blood clotting
Updated: August 31, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortFibrinogen is the protein that forms the scaffold of a blood clot and a marker of inflammation. A typical range is 2.0–4.0 g/L (200–400 mg/dL). It rises with inflammation, after surgery and in pregnancy; critically low levels occur in severe clotting consumption.
Reference ranges
Group
Reference range
Adults
2.0–4.0 g/L (200–400 mg/dL)
The source gives a range of 2.0–4.0 g/L (200–400 mg/dL); in pregnancy fibrinogen is physiologically higher. Reference ranges vary between laboratories and assays — use the range printed on your own lab report.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
Fibrinogen (clotting factor I) is a soluble plasma protein made in the liver. When a vessel is injured, thrombin converts fibrinogen into insoluble fibrin strands that form the scaffold of the clot stopping the bleeding.
Fibrinogen is also an acute-phase protein: its level rises markedly with inflammation, infections, after surgery and during pregnancy, so a moderate increase is a common, non-specific finding. Persistently high fibrinogen is treated as a cardiovascular risk factor, while critically low levels signal severe clotting disorders such as DIC or massive blood loss.
When it is high
Inflammation and infectionsAs an acute-phase protein, fibrinogen rises in pneumonia, rheumatic diseases and flares of chronic inflammation.
PregnancyA physiological rise — the body prepares for delivery and possible blood loss.
After surgery and traumaA typical response to tissue injury; the level normalizes with recovery.
Cardiovascular riskPersistent moderate elevation is linked to increased clotting tendency and atherosclerosis.
When it is low
DICMassive consumption of clotting factors in severe illness sharply lowers fibrinogen — an emergency.
Severe liver diseaseThe liver fails to synthesize the protein — fibrinogen falls with other factors.
Inherited afibrinogenemiaA rare inherited absence or defect of the protein; presents with bleeding from childhood.
Massive blood loss and transfusionsPlasma dilution and protein loss with blood lower the level.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Inflammation and infectionsPregnancyRecent surgerySmoking
How to prepare
Blood is drawn into a citrate tube, preferably in the morning while fasting. Skip intense workouts the day before. Since fibrinogen responds to any inflammation, a 'baseline' level is best measured outside colds and flare-ups.
When a retest makes sense
If abnormal — after the cause (inflammation) resolves, usually in 2–4 weeks; in pregnancy — on the obstetrician's schedule.
Who usually reviews this result
A result outside the reference range is usually reviewed by: hematologist or GP; in pregnancy — obstetrician-gynecologist. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: FibrinogenFactor IClauss fibrinogen
Units and conversion
Measured in: g/L
g/L=mg/dL
mg/dL = g/L × 100. Example: 2.0 g/L = 200 mg/dL. Results are rounded to 2 decimal places.
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
Does fibrinogen of 4.5 g/L (450 mg/dL) mean clots?
No. A moderate rise most often reflects inflammation or recent strain on the body, not an existing clot. Doctors weigh it together with CRP, D-dimer and the clinical picture.
Why is fibrinogen high in pregnancy?
It is a normal adaptation: by the third trimester the level clearly exceeds the non-pregnant reference, protecting against delivery blood loss. Interpretation belongs to the obstetrician.
Can fibrinogen be lowered?
There is no pill 'for fibrinogen' — the cause is treated (inflammation, metabolic issues). Quitting smoking and controlling weight, glucose and blood pressure reduce the associated vascular risk.
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