Fibrinogen
Clotting factor I: a liver protein needed to form blood clots
Also known as
Definition
Fibrinogen is a protein made by the liver and, as clotting factor I, one of the coagulation factors in the blood. After an injury, the clotting factors work together in a chain reaction so that a stable blood clot forms and the bleeding stops. The blood test measures how much fibrinogen is present in your blood. The value can also change with infections and inflammation.
| Parameter | Value |
|---|---|
| Unit | mg/dl or g/l |
| Reference Range | Typical for adults: 200–400 mg/dl (2.0–4.0 g/l). Labs and methods differ slightly; the range printed on your own report is what counts. Discuss any deviation with your doctor. |
Agree on your personal target range with your doctor.
100 mg/dl equals 1 g/l.
↓ What a low value means
A low fibrinogen level can be linked to an inherited or acquired fibrinogen deficiency, increased consumption, for example in disseminated intravascular coagulation (DIC), increased breakdown of fibrin (fibrinolysis) or heavy blood loss. Severe liver disease can also impair the production of clotting factors. Too few clotting factors can go along with a greater tendency to bleed; discuss any deviation with your doctor.
↑ What a high value means
A raised fibrinogen level can be linked to infections or inflammation. Higher levels of clotting factors can in general go along with a greater tendency to clot; whether that applies is clarified by further tests. Your doctor interprets the result together with other coagulation and inflammation markers.
When to test
Fibrinogen is mainly measured when there are problems with blood clotting, such as excessive bleeding, or when clotting tests such as PT/INR or aPTT were abnormal. Clotting disorders in the family can also be a reason. No special preparation is needed.
Frequently asked questions
Is fibrinogen an inflammation marker? +
Fibrinogen is first and foremost a clotting factor. Its level can, however, also change with infections or inflammation. Your doctor uses further values to interpret it.
How does fibrinogen relate to PT/INR and aPTT? +
PT/INR and aPTT measure how long your blood takes to clot. If one of these tests is abnormal, individual clotting factors such as fibrinogen can be measured specifically to narrow down the cause.
Do I need to prepare for the test? +
No, no special preparation is needed. If you have a known bleeding tendency or take anticoagulant medicines, mention it before the blood draw.
What does clotting factor I mean? +
Clotting factors carry a Roman numeral as well as a name. Fibrinogen is factor I, prothrombin is factor II. Together they work in a chain reaction that ends with a blood clot stopping the bleeding.
Fibrinogen
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.