What this test measures
Fibrinogen is a large plasma glycoprotein synthesised by the liver. When the coagulation cascade is activated, thrombin converts fibrinogen into fibrin, which polymerises to form the structural mesh of a blood clot. The Clauss fibrinogen assay measures functional fibrinogen by adding excess thrombin and measuring clotting time.
Normal adult range is 200–400 mg/dL. Fibrinogen is also an acute-phase reactant — it rises in inflammation, infection, malignancy, pregnancy (reaches 400–600 mg/dL in late pregnancy), and after trauma or surgery. Persistently elevated fibrinogen is an independent cardiovascular risk factor. Low fibrinogen (<150 mg/dL) impairs clotting and raises bleeding risk; <100 mg/dL is a critical level that often needs cryoprecipitate or fibrinogen concentrate transfusion.
Why it matters
Fibrinogen is essential in the workup and management of: (1) Disseminated Intravascular Coagulation (DIC) — sepsis, obstetric emergencies (postpartum haemorrhage, abruption), major trauma — where fibrinogen falls dramatically; (2) Severe liver disease — fibrinogen is one of the last clotting factors to fall but its drop signals advanced hepatic failure; (3) Massive haemorrhage protocols — current trauma and obstetric guidelines target fibrinogen >150–200 mg/dL during active bleeding; (4) Cardiovascular risk assessment — persistently high fibrinogen contributes to cardiovascular risk; (5) Thrombolytic therapy monitoring — fibrinogen falls dramatically with streptokinase / tenecteplase.
In Indian obstetric practice, postpartum haemorrhage from abruption or amniotic fluid embolism often involves rapid fibrinogen consumption — early fibrinogen replacement is now a cornerstone of major obstetric haemorrhage protocols.
How to prepare
No fasting required. Disclose pregnancy, recent surgery, active infection, malignancy, liver disease, current anticoagulation, thrombolytic therapy, and any acute bleeding. The blood sample must be in a citrate tube and processed within 4 hours.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Fibrinogen (mg/dL)[1][2] | 200–400 mg/dL (rises in pregnancy to 400–600) | Low fibrinogen (<150 mg/dL) — bleeding risk. Causes: DIC (consumption), severe liver disease (decreased synthesis), thrombolytic therapy, congenital afibrinogenaemia / hypofibrinogenaemia (rare), dilutional after massive transfusion. <100 mg/dL is critical and typically needs cryoprecipitate or fibrinogen concentrate. | High fibrinogen (>400 mg/dL) — acute-phase reactant. Causes: inflammation, infection, malignancy, pregnancy (normal physiology), trauma, post-operative state, smoking, oral contraceptives. Persistently high values are an independent cardiovascular risk factor. |
Fibrinogen interpretation
| Fibrinogen (mg/dL) | Status | Implication |
|---|---|---|
| > 400 | Elevated | Inflammation, infection, pregnancy, malignancy, smoking; CV risk if sustained |
| 200 – 400 | Normal | — |
| 150 – 200 | Low end of normal | Watch in active bleeding (trauma, obstetric); supplementation considered |
| 100 – 150 | Reduced | Bleeding risk increased; cryoprecipitate or fibrinogen concentrate often needed |
| < 100 | Critical | Major bleeding risk; emergency fibrinogen replacement |
Frequently asked questions
When is fibrinogen tested?
In DIC suspected from sepsis or obstetric emergency; in severe liver disease; in massive haemorrhage protocols; when monitoring thrombolytic therapy; and in some cardiovascular risk assessments.
Do I need to fast?
No.
My fibrinogen is 600 — should I worry?
Mildly elevated fibrinogen is common with infection, pregnancy, smoking, oral contraceptives, or chronic inflammation. Persistently high values (>400 sustained over weeks) are an independent cardiovascular risk factor. In pregnancy 600 is normal.
Why is fibrinogen important in obstetric haemorrhage?
In postpartum haemorrhage, fibrinogen drops faster than other clotting factors and predicts severity. Modern obstetric massive transfusion protocols target fibrinogen >200 mg/dL during ongoing bleeding, with cryoprecipitate or fibrinogen concentrate.
Is fibrinogen the same as factor I?
Yes — fibrinogen is coagulation factor I.
Can DOACs affect the result?
Direct thrombin inhibitors (dabigatran) can interfere with Clauss fibrinogen assay, giving falsely low values. The lab should be informed of any DOAC use.
Does pregnancy affect fibrinogen?
Yes — fibrinogen rises gradually through pregnancy from baseline 250–350 to 400–600 mg/dL by term. This is normal physiology and provides bleeding protection at delivery.
How fast is the report?
Most NABL labs report fibrinogen within 2–4 hours.
Related Coagulation tests
Tests commonly ordered alongside FIBRINOGEN, or that help interpret an unexpected result.
Sources & references
- NCBI StatPearls — Fibrinogen · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Fibrinogen Test · accessed 2026-05-30T00:00:00.000Z
- ISTH — Fibrinogen Standardisation · accessed 2026-05-30T00:00:00.000Z
- BSH — Major Haemorrhage and Massive Transfusion · accessed 2026-05-30T00:00:00.000Z
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