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.
Low fibrinogen levels can also 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.
A fibrinogen activity test may be ordered alone or as part of a series of tests to determine the cause of abnormal bleeding.
Your doctor may order a fibrinogen activity test if you’re experiencing any of the following:
- excessive bruising
- excessive bleeding from the gums
- frequent nosebleeds
- hemorrhage of the gastrointestinal tract
- blood in the urine
- blood in the stool
- bleeding in the head
- rupture of the spleen
Tests may also be ordered if you have:
- abnormal results from a prothrombin time test or partial thromboplastin time test
- symptoms of disseminated intravascular coagulation, which is a condition in which small clots form throughout the body
- signs of an abnormal breakdown of fibrinogen (fibrinolysis)
- a possible acquired or inherited factor deficiency that affects how your blood clots
A fibrinogen activity test may also be part of a general evaluation of your risk of cardiovascular disease. People with clotting disorders can have an increased risk of heart disease and stroke.
There are no special preparations necessary for this test. Your doctor may advise you to stop taking certain medications before this test. It’s very important that you inform your doctor if you’re taking any blood thinners.
A healthcare provider will take a sample of blood from your arm. They’ll clean the site with a swab of rubbing alcohol. They’ll insert the needle into a vein, and a tube will be attached to collect the blood. The needle will be removed when enough blood has been drawn. The site will then be covered with a gauze pad.
This blood sample will be sent to a laboratory for analysis.
The normal level of fibrinogen in the blood is between 1.5 to 3.0 grams per liter.
Abnormal results may be higher or lower than the reference range. Abnormal results can be caused by:
- excessive fibrinogen use
- acquired or inherited fibrinogen deficiency
- abnormal fibrinolysis
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.
As with any blood test, there are minimal risks. These include the following:
- You may have minor bruising at the needle site.
- In very rare cases, the vein may also become swollen after blood is drawn. Applying a warm compress several times per day can treat this condition, which is known as phlebitis.
- Ongoing bleeding could be a problem if you have a bleeding disorder or if you’re taking blood thinners, such as warfarin (Coumadin) or aspirin.
- Puncture site infection is another potential complication, noted by red swelling and possible pus formation.
After the Test
If you have a fibrinogen deficiency, your doctor may prescribe factor replacement treatment to control or stop the bleeding. This involves receiving fibrinogen blood products or substitutes through your veins.
This form of treatment should be used to increase your fibrinogen level to 1 gram per liter if you’re experiencing mild bleeding. If you’re having severe bleeding or undergoing surgery,
your levels should be increased to 2 grams per liter.
Fibrinogen concentrate may also be administered at the following times:
- during surgery
- during delivery or after childbirth
- before dental surgery
- after trauma
- to prevent bleeding