Fibrinogen: what it is, what it tells you and when it’s tested

Fibrinogen is a protein made by your liver. When you are injured, it turns into fibrin, the mesh that holds a clot together and stops the bleeding. It also rises when there is inflammation in your body.

When it’s tested

Doctors mostly order it to see how well your blood clots: before surgery, if you bleed easily, if you have liver disease or, in hospital, during heavy bleeding. Sometimes it is also used to look for inflammation.

It is not a routine test for people who feel well. A high fibrinogen is linked to a higher risk for your heart and arteries, but adding it to cholesterol, blood pressure and smoking barely changes the risk estimate.

That is why Rosa does not test it. For inflammation it measures high-sensitivity CRP. For your heart it measures LDL cholesterol, ApoB and lipoprotein(a).

What it tells you, and what it does not

If it is low, your blood may clot less well. This happens with some liver diseases, after major bleeding or, rarely, with an inherited condition.

If it is high, there is often inflammation. Smoking, extra weight, diabetes and age raise it too. It does not say where the inflammation is, though, or whether you will get a clot.

If it is normal, your blood usually has enough fibrinogen to clot.

That is why it is read together with other tests:

• High-sensitivity CRP: It shows whether there is inflammation
• Platelets: The other half of a clot
• INR: It shows how fast your blood clots
• Albumin: Your liver makes it too: if both are low, the liver is checked

Normal fibrinogen levels

The lab decides what is normal. Many lab reports give 200 to 400 mg/dL. Some labs use slightly different limits.

If your report uses g/L, divide by 100: 400 mg/dL is 4 g/L.

It rises with age and in pregnancy, especially in the last months.

What your result means

Find the row for your result, in mg/dL. Which values need a doctor? Below 200 or above 400.

• Below 200: Low. Your liver is making less, or your body is using it up, for example after heavy bleeding. Rarely it is inherited. Talk to your doctor. If you have heavy bleeding that will not stop, call 112 or go to the emergency department.
• 200 to 400: Normal. Your blood has enough fibrinogen to clot well, and there is no sign of significant inflammation. Nothing to do.
• Above 400: High. Often there is inflammation or an infection. Smoking, extra weight, diabetes, age and pregnancy raise it too. Show your report to your doctor. They usually look at CRP too.

If your fibrinogen is high or low

• High fibrinogen: Usually there is inflammation. Smoking, weight and diabetes count too.
• Low fibrinogen: Less common. It can come from the liver or from bleeding, and always needs a doctor to look at it.

What can skew the result

A few things change it for a while, without any disease.

• A recent infection: Even a cold or flu raises it for a few weeks.
• Pregnancy: It rises on its own in pregnancy. That is normal.
• Smoking: People who smoke usually have higher levels.
• Some medicines: Some anticoagulants and some hospital treatments can skew the result. Tell your doctor.

When to worry

Talk to your doctor if:

• Your fibrinogen is below 200 mg/dL, or below the limit on your report.
• It is above 400 and stays high on a second check.
• You bruise for no reason, have nosebleeds or bleeding gums that will not stop, or very heavy periods.
• You are bleeding heavily and cannot stop it: call 112 or go to the emergency department.

Frequently asked questions

What are normal fibrinogen levels? Many lab reports give 200 to 400 mg/dL, which is 2 to 4 g/L. The range on your own report is what counts.

Do I need to fast for a fibrinogen test? Usually not. If you have other tests at the same time, such as glucose or cholesterol, follow the instructions for those.

What is the difference between fibrinogen and CRP? Both rise with inflammation. CRP is faster and more sensitive, so it is used more. Fibrinogen is mainly used to see how well your blood clots.

Is high fibrinogen in pregnancy normal? Yes, it rises on its own in pregnancy, especially in the last months. Your gynaecologist knows how to read it for your stage of pregnancy.

Does Rosa test fibrinogen? No. For inflammation Rosa measures high-sensitivity CRP, for your heart cholesterol, ApoB and lipoprotein(a), and it also measures platelets. If your doctor wants fibrinogen, they order it separately.

Sources

• Fibrinogen Studies Collaboration, plasma fibrinogen level and the risk of major cardiovascular diseases and nonvascular mortality: an individual participant meta-analysis. JAMA, 2005. PMID 16219884
• Emerging Risk Factors Collaboration, C-reactive protein, fibrinogen, and cardiovascular disease prediction. New England Journal of Medicine, 2012. PMID 23034020
• Kamath and Lip, fibrinogen: biochemistry, epidemiology and determinants. QJM, 2003. PMID 14500858
• Mackie and colleagues, guidelines on fibrinogen assays. British Journal of Haematology, 2003. PMID 12716361