Blood Health

Fibrinogen Activity

Optimal Result: 193 - 507 mg/dL.

A fibrinogen activity test is also known as a Factor I assay. It’s used to determine the level of fibrinogen in your blood. Fibrinogen, or factor I, is a blood plasma protein that’s made in the liver. Fibrinogen is one of 13 coagulation factors responsible for normal blood clotting.

When you start to bleed, your body initiates a process called the coagulation cascade, or clotting cascade. This process causes coagulation factors to combine and produce a clot that will stop the bleeding. If you don’t have enough fibrinogen or if the cascade isn’t working normally, clots will have difficulty forming. This can cause excessive bleeding.

Fibrinogen is measured in milligrams per deciliter (mg/dL):

- A normal value for fibrinogen is between 200 and 400 mg/dL.

- A fibrinogen value of less than 50 mg/dL may mean you're in danger of bleeding after surgery.

- A fibrinogen value of more than 700 mg/dl may mean you're in danger of forming clots that could harm your heart or brain. 


What does it mean if your Fibrinogen Activity result is too low?

Low fibrinogen levels can cause thrombosis due to an increase in coagulation activity. Thrombosis refers to the formation of a blood clot inside of a blood vessel. The clot blocks the normal flow of blood through the circulatory system. This can lead to serious medical conditions such as heart attack and stroke.

The three types of fibrinogen deficiency are afibrinogenemia, hypofibrinogenemia, and dysfibrinogenemia:


Afibrinogenemia is the total absence of fibrinogen. This disorder affects 5 out of every 10 million people. This disorder causes the most severe bleeding out of the three forms of fibrinogen deficiency.


Hypofibrinogenemia is an abnormally low level of fibrinogen. In this case, the test would show a level between 0.2 and 0.8 grams per liter. This form of the deficiency is less common than afibrinogenemia and it can cause mild to severe bleeding.


Dysfibrinogenemia is a condition in which fibrinogen levels are normal, but the protein doesn’t function properly. Dysfibrinogenemia affects only about one in every 1 million people. The condition rarely causes a bleeding problem and instead is more likely to cause thrombosis.

What does it mean if your Fibrinogen Activity result is too high?

High fibrinogen values may also be associated with:

  • Infections and inflammation

  • Cancer

  • Rheumatoid arthritis

  • Nephrotic syndrome

  • Heart attack

  • Stroke

  • Pregnancy 

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