Fibrinogen blood test: functions and results

The level of fibrinogen in the blood is directly related to the coagulation process; however, alterations in values ​​can be associated with disease.

Last update: 15 January, 2022

The blood fibrinogen test, also known as “factor I activity,” is used to determine the levels of this substance that is related to coagulation.

The normal level should be between 200 and 400 milligrams per deciliter (mg/dl) of blood. However, this varies somewhat with the age of the person. In fact, in children under five years of age it is usually a little lower.

Now the test results they can denote if there is a deficiency or, on the contrary, an elevated level of fibrinogen in the blood. In turn, this increase or decrease is related to various factors, such as diseases, pregnancy, menopause, drug use, among others.

What is fibrinogen and what is its function?

There has always been great interest in understanding coagulation. In ancient times it was thought that this process was due to solidification by cooling. It is at the beginning of the 20th century, with the publication of a study by Paul Morawitz, when research on the matter is refocused.

Fibrinogen or Factor I is a protein synthesized in the liver that is incorporated into blood plasma. It is part of the group of coagulation factors, along with prothrombin, calcium, tissue factor, among others. They are 13 in total.

Therefore, it is one of those responsible for stopping bleeding when there is a wound or bleeding. This complex process is known as “hemostasis” or “coagulation cascade.”

During it, thrombin helps convert fibrinogen to fibrin, which works like a cement and forms a mesh or network. In turn, the platelets stick together—like bricks—to produce a clot that plugs the wound.

In the opposite process, fibrinolysis, fibrin activates an enzyme that breaks down clots (called plasmin), and fibrinogen inhibits it. In this way, it is ensured that everything happens in an ideal way; clots break down when they are no longer required and do not form unnecessarily.

As some know, blood clots can be harmful; if they block the blood vessels, it would cause a heart attack or stroke. Thus, the balance between blood fibrinogen and fibrin is paramount.

In addition to this, fibrinogen is considered to bind and activate white blood cells, which is why it plays an important role in the immune response to infection or injury.

Some recent findings seem to confirm this. For example, in an investigation with patients presenting with sepsis, rapid recovery and lower mortality were correlated with an increase in fibrinogen.

In another laboratory study with mice suffering from acetaminophen-induced liver damage, it was found that fibrinogen can help repair the liver by activating white blood cells.

Fibrinogen is part of the coagulation factors.

How and why is the fibrinogen blood test done?

The blood fibrinogen test is done to estimate how well the clotting process is working. Often fasting for up to 12 hours is suggested. Even if special preparations are not required, the doctor may recommend that some medication, especially anticoagulants, be stopped beforehand.

To perform the test a serum sample is taken directly from the vein (can be ulnar or cephalic) with a syringe. The needle is removed when enough blood (approximately 2 cubic centimeters) has been drawn.

A standard amount of thrombin is then added to the sample and the time it takes for the fibrin clot to form is measured. This makes it possible to determine the quantity, but not the activity of fibrinogen in the blood.

This period correlates directly proportionally with the amount of active fibrinogen in the sample. Therefore, prolonged clot formation times may be due to decreased fibrinogen concentrations, or, to a dysfunction of the same.

Test risks

Obtaining a blood sample may be more difficult for some people than for others. However, the blood fibrinogen test is a simple, fast and safe process; carries no risks or significant side effects. Only a slight pain is experienced with the puncture and a bruise after it. These symptoms disappear after a little while (one or two days).

When to do the fibrinogen blood test?

Your doctor may order a fibrinogen blood test, alone or as part of a series of tests, when there are abnormal bleeding or clotting conditions. Among other circumstances, the option is considered in any of the following cases:

  • Frequent nosebleeds.
  • Heavy menstrual bleeding.
  • Presence of blood in urine or stool.
  • Abnormal bleeding from the gums.
  • Gastrointestinal tract bleeding.
  • Bruises for no apparent reason.
  • Rupture of the spleen.
  • Thrombosis.
  • Abnormal prothrombin or partial thromboplastin test results.
  • Disseminated intravascular coagulation symptoms.
  • Abnormal fibrinolysis.
  • Inherited or acquired dysfunction related to coagulation.

On the other hand, the blood fibrinogen test allows to know if the decrease in the activity of this protein is due to an insufficient quantity or to a dysfunction; it also serves to monitor coagulation capacity over time.

Along with other tests, it also helps assess the risk of developing cardiovascular disease, peripheral arterial disease, or heart attack.

What do the results mean?

The expected level of fibrinogen in the blood is 200 to 400 milligrams per deciliter (mg/dl), but this can vary somewhat with age. In fact, in children under five years of age it is lower, 160 to 400 mg/dl. And in newborns or babies under one year old it ranges between 80 and 90 up to 375 or 385 mg/dl.

Now, when the results are not within this range, they are considered to be higher or lower than expected. Let’s look at each one separately.

High levels

In this case, we have the following reference scale (in adults):

  • 400 – 600 mg/dl (slightly high): It may be due to circumstantial factors. A new analysis must be carried out a few weeks later to see if the values ​​return to normal.
  • 600 – 700 mg (moderately high): it is convenient to consult with the doctor. If blood pressure is also high, the risk of stroke increases.
  • More than 700 mg/dl (excessively high): high chance of blood clots forming and damaging the heart or brain.

Low levels

There are three types of fibrinogen deficiency in the blood:

  • Afibrinogenemia or total absence of fibrinogen: it is rare (affects 1 person in 2 million). Although it does not necessarily cause bleeding, when it does occur it is severe.
  • Hypofibrinogenemia: low fibrinogen levels, below 200 mg/dl. It is associated with minor bleeding.
  • Dysfibrinogenemia: blood levels are normal, but fibrinogen is not working properly. It can be congenital or acquired and affects one person in a million. It causes bleeding and thrombosis.

Why is fibrinogen in the blood altered?

Factor I disturbance may be temporary. In this case, possible related factors include pregnancy (causes the increase), menstruation, bleeding, a blood transfusion or drug reactions.

Among the drugs that alter the levels of this protein, the following are mentioned:

  • oral contraceptives
  • Estrogens.
  • steroids.
  • Antitubercular.
  • Antiandrogens.
  • Aspirin.
  • Warfarin.
  • Various medications to lower cholesterol.

On the other hand, the low level of fibrinogen in the blood can be caused by factors such as menopause or tobacco use, as well as medical conditionswhether hereditary or acquired. Among the latter are the following:

  • Tumors.
  • Severe malnutrition.
  • Nephrotic syndrome.
  • Inflammatory disorders (such as rheumatoid arthritis.
  • End-stage liver disease.

However, the altered values ​​reflected in the test are not typically used to provide relevant diagnostic information about an illness or disease.

Fibrinogen in the blood is altered by various conditions and pathologies. Therefore, if its levels are altered, the doctor suggests carrying out additional tests.

Associated disorders

Maintaining altered values ​​of fibrinogen in the blood should be monitored, since it can increase the risk of developing various diseases. If levels are low and bleeding from wounds does not stop or takes a long time, the chances of infection increase.

On the contrary, high levels promote blood clotting, even when it is not necessary. Thus, there are more chances of cardiovascular problems, since thrombi are formed, which can trigger heart attacks or embolisms.

Normalization of fibrinogen in the blood

When the increase in fibrinogen is due to pregnancy or is caused by an inflammatory process, the levels will return to normal once the underlying problem is resolved. Anyway, In some cases, treatment is required..

For example, depending on the cause of the problem, bezafibrate or replacement therapy with substitute blood products may be prescribed.

If there is a risk of cardiovascular diseases, lifestyle changes are recommended such as a diet rich in omega 3, physical exercise and quitting tobacco and alcohol consumption.

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