Fibrinogen Test: Normal Range, Causes & Risks

A patient came to me recently concerned about recurrent nosebleeds and easy bruising. Her blood work revealed a low fibrinogen level — a finding that often raises questions about liver health or bleeding risks. Fibrinogen, also known as factor I, is a protein produced by the liver that plays a central role in blood clotting. Testing it helps us evaluate bleeding disorders, monitor liver function, and assess inflammation.

What Is Fibrinogen?

Fibrinogen is a soluble plasma protein that, when activated by thrombin, converts into fibrin — the mesh that stabilises a blood clot. It is an acute-phase reactant, meaning its levels rise during inflammation or tissue injury. In my clinical practice, I often use fibrinogen levels as a marker for both clotting ability and inflammatory burden.

Why Is a Fibrinogen Test Ordered?

Doctors request a fibrinogen test for several reasons:

• Unexplained bleeding or excessive bruising
• Prior to surgery, especially if clotting disorders are suspected
• Monitoring liver disease (since the liver produces fibrinogen)
• Evaluating disseminated intravascular coagulation (DIC)
• Assessing cardiovascular risk — elevated levels correlate with heart attack and stroke

Fibrinogen Reference Ranges

Normal fibrinogen levels vary by laboratory, but typical values are between 200 and 400 mg/dL. The table below shows common reference ranges by age and physiological state.

Note: Ranges may differ between labs. Always consult your physician for interpretation. The LOINC code for fibrinogen is 3255-7.

High Fibrinogen Levels: Causes and Implications

Elevated fibrinogen (hyperfibrinogenemia) is common in acute and chronic inflammation. My patients with rheumatoid arthritis, infections, or post-surgical states often show raised levels. Other causes include:

• Smoking
• Obesity
• Diabetes
• Coronary artery disease
• Cancer

High fibrinogen increases blood viscosity and clot formation, raising the risk of stroke and heart attack. Lifestyle changes — such as smoking cessation and weight loss — can help lower levels.

Low Fibrinogen Levels: Causes and Risks

Low fibrinogen (hypofibrinogenemia) may signal a bleeding tendency. Common causes include:

• Liver cirrhosis or severe hepatitis
• Disseminated intravascular coagulation (DIC)
• Congenital deficiency (rare)
• Malnutrition or end-stage kidney disease

Patients with low fibrinogen often present with prolonged bleeding from cuts, easy bruising, or heavy menstrual periods. Treatment involves addressing the underlying cause and, in severe cases, cryoprecipitate or fibrinogen concentrates.

Fibrinogen During Pregnancy

During pregnancy, fibrinogen levels rise progressively, especially in the third trimester, to prepare the body for childbirth-related bleeding. This is a normal physiological change. However, extremely high levels (above 600 mg/dL) may increase the risk of thrombosis. If you are pregnant and concerned about your clotting profile, your obstetrician will monitor fibrinogen as part of routine coagulation tests.

How to Prepare for the Fibrinogen Test

No special preparation is usually needed. A blood sample is drawn from a vein in your arm. Tell your doctor if you are taking blood thinners (e.g., warfarin, heparin) as these can affect results. Fasting is not required, but some labs prefer it for consistency.

Interpreting Your Results

Your fibrinogen level alone rarely provides a diagnosis. It must be evaluated alongside other tests (PT, aPTT, platelet count) and your clinical history. In my practice, I explain to patients that a single elevated reading doesn't automatically mean they have a clot risk — we look at trends and the whole picture.

This article is for educational purposes and does not substitute professional medical advice. Always discuss your lab results with your healthcare provider.