Laboratory test · Men’s health
Fibrinogen: what it is, when it is measured and what a high result means
- Sample: venous blood
- Preparation: fasting not essential
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- Sample
- venous blood
- Preparation
- fasting not essential
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Fibrinogen is a blood plasma protein produced in the liver that is essential for blood clot formation. This test measures how much fibrinogen is in your blood and is most often performed alongside PT and APTT: for a bleeding tendency and before surgery or procedures. Because fibrinogen also rises in inflammation, a high result more often suggests inflammation than a clotting disorder.
Who the test is for
- people prone to bleeding, with bruises without injury, prolonged bleeding after tooth extraction or minor injury, or very heavy periods,
- people before surgery or another procedure, when requested by a surgeon or anaesthetist,
- people with prolonged PT or APTT, to check whether fibrinogen deficiency contributes,
- people with liver disease, because the liver produces fibrinogen,
- people with a family history of an inherited fibrinogen disorder.
What fibrinogen is
Fibrinogen is also called clotting factor I. When a blood vessel is damaged, the enzyme thrombin converts fibrinogen into fibrin strands. These interweave with platelets to form a firm clot that closes the wound. If fibrinogen is insufficient or does not work properly, the clot is weak and bleeding lasts longer.
Fibrinogen is also an acute-phase protein. The liver increases production in response to inflammation, infection or tissue damage, for example after injury or surgery. It remains in the blood for days (its half-life is 3 to 5 days), so can stay elevated for some time after inflammation settles. High fibrinogen also accelerates the erythrocyte sedimentation rate, so these two results are often elevated together.
A doctor usually requests fibrinogen alongside prothrombin time (PT) and APTT.
In hospital, fibrinogen is also monitored during major bleeding and disseminated intravascular coagulation (DIC), in which clotting factors are consumed faster than they are produced. Fibrinogen is not the first choice for monitoring inflammation. For this, CRP and other inflammatory markersare used.
Save with a panel
Test Fibrinogen is also included in these panels.
Preparation and sample
Fibrinogen is measured in citrated plasma. Blood is taken from a vein into a tube with sodium citrate (usually with a light-blue cap), which binds calcium and prevents the blood from clotting in the tube. The tube must be filled to the mark because the blood-to-citrate ratio affects the result.
- Fasting: not required for fibrinogen alone. If glucose, blood lipids or PT are being measured at the same time, come in the morning after fasting. This also applies to all panels containing fibrinogen, because they all include PT.
- Anticoagulant medicines: mention them at blood sampling, because some can affect coagulation results. Do not stop treatment yourself.
- Recent infection or surgery: tell your doctor, because they temporarily raise fibrinogen.
How to read fibrinogen results
Fibrinogen is reported in grams per litre (g/L). In adults, the reference interval is usually approximately 1,8 to 3,5 g/L, but limits depend on the method and laboratory, so the interval printed on your report is the relevant one. A doctor interprets the result alongside PT, APTT, blood count and your symptoms. A value slightly outside the range rarely means much on its own.
High fibrinogen
High fibrinogen most often indicates an inflammatory response in the body. Possible causes include:
- acute infection or inflammation, injury, burns and recovery after surgery,
- chronic inflammatory diseases such as rheumatoid arthritis,
- malignancies and nephrotic syndrome,
- pregnancy and oestrogen-containing medicines such as contraceptive pills,
- smoking, obesity, diabetes and older age.
High fibrinogen alone usually causes no symptoms. In large population studies, people with higher fibrinogen more often developed coronary heart disease and stroke (Fibrinogen Studies Collaboration, JAMA 2005.) but genetic studies have not confirmed that fibrinogen directly causes these diseases. An elevated result is therefore not a diagnosis but a reason for a doctor to investigate the cause and assess other risk factors: blood pressure, cholesterol, glucose and smoking.
Low fibrinogen
Low fibrinogen means the body has less “raw material” for a clot. Possible causes include:
- severe liver disease, when the liver does not produce enough fibrinogen,
- increased consumption in DIC or major bleeding,
- clot-dissolving medicines (thrombolysis) and certain medicines used to treat leukaemia,
- rare inherited disorders in which fibrinogen is absent, insufficient or structurally altered so it works less effectively.
When fibrinogen is very low, approximately below 1 g/L, bleeding tendency increases. Show such a result to a doctor without delay.
How to arrange testing
For a comprehensive clotting assessment, fibrinogen is included in the Coagulation Panel, together with PT and APTT.
Before a procedure, check with the facility which tests are required and how recent results must be, because requirements differ. You can have blood taken without an appointment or referral at one of our branches across Croatia (listed on the Contact page). Prices for all tests and panels are available in the service price list.
Frequently asked questions
Is fibrinogen the same as D-dimer?
No. Fibrinogen is the “raw material” from which a clot is formed, while D-dimers are fragments produced when an existing clot breaks down. D-dimer helps a doctor rule out thrombosis or pulmonary embolism, while fibrinogen shows whether there is enough for normal clotting.
Is high fibrinogen normal during pregnancy?
Yes. Fibrinogen rises gradually during pregnancy and is highest in the third trimester. A value above the adult reference interval is therefore usually not a cause for concern in pregnancy. A gynaecologist interprets it according to the pregnancy week and your health.
How can high fibrinogen be lowered?
There is no medicine prescribed solely to lower fibrinogen. The cause is treated, most often inflammation or infection, after which the value returns towards normal. Smoking and obesity are associated with higher fibrinogen, so stopping smoking and losing weight also help.