The level of fibrinogen in the blood is directly related to the clotting process. However, alterations in values may be associated with the disease.
The fibrinogen blood test, also called “factor I activity,” is used to determine levels of this clotting-related substance.
The normal level should be between 200 and 400 milligrams per deciliter (mg/dl) of blood. However, it varies somewhat with age. In children under five, it is usually a little lower.
The test results may indicate whether there is a deficiency or, conversely, a high level of fibrinogen in the blood. An increase or decrease may be related to illness, 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, this process was thought to be due to solidification by cooling. It was at the beginning of the 20th century, with the publication of a study by Paul Morawitz, that research in this area was refocused.
Fibrinogen or factor I is a protein synthesized in the liver which is incorporated into the blood plasma. It is part of the group of coagulation factors, with prothrombin, calcium, tissue factor, among others. There are 13 in all.
It is therefore one of those responsible for stopping bleeding in the event of a wound or haemorrhage. This complex process is called “haemostasis” or “coagulation cascade”.
During this one, thrombin helps convert fibrinogen to fibrin, which acts as a cement and forms a mesh or network. In turn, the platelets stick together, like bricks, to produce a clot that seals the wound.
In the opposite process, which is fibrinolysis, fibrin activates a clot-breaking enzyme (called plasmin) and fibrinogen inhibits it. Clots break down when they are no longer needed and do not form unnecessarily.
As some know, clots can be harmful. If they block blood vessels, it would lead to heart attack or stroke. As a result, the balance between blood fibrinogen and fibrin is paramount.
In addition to this, fibrinogen is believed to bind and activate white blood cells, thus playing an important role in the immune response to infection or injury.
Some recent discoveries seem to confirm this. For example, in a survey of patients with sepsis, rapid recovery and lower mortality were correlated with increased fibrinogen.
In another laboratory study conducted on mice with acetaminophen-induced liver damage, it was found that fibrinogen can help repair the liver by activating white blood cells.
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How and why is fibrinogen assayed?
The fibrinogen blood test is done to estimate how well the coagulation process is working. Often it is recommended to perform it on an empty stomach up to 12 hours. Even if prior preparation is not required, the doctor may recommend stopping taking a drug, especially if it is an anticoagulant.
To perform the test, a serum sample is taken directly from the vein (it can be ulnar or cephalic) using a syringe. The needle is removed when enough blood (about 2 cc) has been drawn.
Next, a standard amount of thrombin is added to the sample and the time required for the formation of the fibrin clot is measured. This determines the amount, but not the activity, of fibrinogen in the blood.
This period is directly proportionally correlated with the amount of active fibrinogen in the sample. Prolonged clot formation times may be due to decreased fibrinogen concentrations or fibrinogen dysfunction.
The risks of dosage
Obtaining a blood sample may be more difficult for some people than for others. However, the fibrinogen blood test is a simple, quick and safe process; it has no major risks or side effects. A slight pain is felt at the time of the puncture, and a bruise then appears. These symptoms disappear after one or two days.
When should the fibrinogen blood test be performed?
The doctor may order a blood test for fibrinogen, alone or as part of a series of tests, in case of abnormal bleeding or clotting conditions. Among other circumstances, this test is considered in any of the following cases:
- Frequent nosebleeds
- Heavy menstrual bleeding
- Presence of blood in urine or feces
- Abnormal bleeding in the gums
- Bleeding from the gastrointestinal tract
- Bruising for no apparent reason
- rate break
- Thrombosis
- Abnormal prothrombin or partial thromboplastin test results
- Disseminated intravascular coagulation symptoms
- Abnormal fibrinolysis
- Hereditary or acquired dysfunction related to coagulation
In addition, the blood assay of fibrinogen makes it possible to know whether the decrease in the activity of this protein is due to an insufficient quantity or to a dysfunction. It is also used to monitor clotting ability over time.
Along with other tests, it also helps assess the risk of developing cardiovascular disease, peripheral arterial disease, or heart attack.
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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 children under five years of age, it is lower, it fluctuates between 160 and 400 mg/dl. And in newborns or babies under one year old, it varies between 80 and 90 up to 375 or 385 mg/dl.
When the results fall outside this range, they are considered above or below expectations. Let’s see the two scenarios.
High levels
In this case, there is the following reference scale (in adults):
- 400 – 600 mg/dl (slightly high): this case may be due to circumstantial factors. A new analysis should be performed weekly to see if the values return to normal.
- 600 – 700 mg (moderately high): it is advisable to consult a doctor. If the blood pressure is also high, the risk of stroke increases.
- More than 700 mg/dL (excessively high): there is a high risk of clots forming that damage the heart or brain.
Low levels
There are three types of fibrinogen deficiency in the blood:
- Afibrinogenemia or complete absence of fibrinogen: this disease is rare (affects one in 2 million people). Although it does not necessarily cause bleeding, this disease is serious.
- Hypofibrinogenemia: low fibrinogen levels, less than 200 mg/dl. This scenario is associated with minor bleeding.
- Dysfibrinogenemia: blood levels are normal, but fibrinogen is not working properly. This disease can be congenital or acquired and affects one in a million people. It causes bleeding and thrombosis.
Why is fibrinogen in the blood altered?
Factor I abnormality may be temporary. In this case, possible associated factors include pregnancy (supportive of augmentation), menstruation, bleeding, blood transfusion, or drug reactions.
Drugs that alter levels of this protein include the following:
- Oral contraceptives
- Estrogens
- Steroids
- Antituberculosis
- Antiandrogens
- Aspirin
- Warfarin
- Various medications to lower cholesterol
On the other hand, low fibrinogen in the blood can be caused by menopause or smoking, as well as hereditary or acquired diseases. Among these 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 generally not used to provide relevant diagnostic information about a condition or disease.
Associated disorders
Maintaining altered fibrinogen values in the blood should be monitored, as 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. As a result, there is a greater risk of cardiovascular problems, as thrombi form, which can lead to heart attacks or embolisms
Normalization of fibrinogen in the blood
When the increase in fibrinogen is due to pregnancy or caused by an inflammatory process, levels will return to normal once the underlying cause is resolved.
In some cases, treatment is necessary. Bezafibrate or replacement therapy with substitute blood products may be prescribed.
If there is a risk of cardiovascular disease, lifestyle changes are recommendedsuch as a diet rich in omega-3s, physical exercise and stopping tobacco and alcohol consumption.
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