A fibrinogen activity test is also known as a factor I assay. It is used to determine the level of fibrinogen in your blood. Fibrinogen, or factor I, is a blood plasma protein that is made in the liver. It 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. This causes coagulation factors to combine and produce a clot that will stop bleeding. If you have insufficient fibrinogen, or the cascade is not working normally, clots will have difficulty forming. This can cause excessive bleeding.
Low fibrinogen levels can also cause thrombosis due to increase in coagulation activity. Thrombosis is the formation of a blood clot inside a blood vessel. The clot bocks 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 are suffering from any of the following symptoms:
- 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 (DIC) – a condition where small clots form throughout the body
- signs of abnormal breakdown of fibrinogen (fibrinolysis)
- a possible acquired or inherited factor deficiency affecting your clotting
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. However, your doctor may advise you to stop taking certain medications before this test. It is very important that you inform your doctor if you are taking any blood-thinning medications.
Your doctor will take a sample of blood from your arm. First, the site will be cleaned with a swab of rubbing alcohol. The needle will then be inserted into a vein, and a tube will be attached to collect the blood.
When enough blood has been drawn, the needle will be removed. The site will then be covered with a gauze pad.
This blood sample is sent to a laboratory for analysis.
The normal level of fibrinogen in the blood is from 2 to 4 g/l.
Abnormal results may be higher or lower than the reference range. They can be caused by:
- excessive fibrinogen use
- acquired or inherited fibrinogen deficiency
- abnormal fibrinolysis
This is the total absence of fibrinogen. According to the Canadian Hemophilia Society, this disorder affects five out of every 10 million people (CHS, 2004). Of the three forms of fibrinogen deficiency, this one causes the most severe bleeding.
This is an abnormally low level of fibrinogen. In this case, the test would show a level between 0.2 g/l and 0.8 g/l. This form of the deficiency is less common that afibrinogenemia. It can cause mild to severe bleeding.
In this condition, fibrinogen levels are normal but the protein doesn’t function properly. Dysfibrinogenemia affects only about one person in every 1 million according to the Canadian Hemophilia Society (CHS, 2012). The condition rarely causes a bleeding problem. Instead, it is more likely to cause thrombosis.
As with any blood test, there are minimal risks.
You may experience minor bruising at the needle site. In very rare cases, the vein may also become swollen after blood is drawn. This condition, known as phlebitis, can be treated with a warm compress several times each day.
Ongoing bleeding could be a problem if you suffer from a bleeding disorder or if you are taking blood-thinning medication, such as warfarin (Coumadin) or aspirin.
If you have a fibrinogen deficiency, your doctor may prescribe factor replacement treatment to control or stop bleeding. This involves intravenous supplementation with fibrinogen blood products or substitutes.
This form of treatment should be used to increase your fibrinogen level to 1 g/L if you are experiencing mild bleeding. If you are experiencing severe bleeding or undergoing surgery,
your levels should be increased to 2 g/L.
Fibrinogen concentrate may also be administered:
- during surgery
- during delivery or after childbirth
- before dental surgery
- after trauma
- to prevent bleeding