• Fibrinogen is a clotting factor – a protein that your body makes to help your blood clot.
• A fibrinogen test can be ordered when doctors want to check whether your blood can form a proper clot—especially if there is a suspicion of a bleeding or clotting problem.
• It may also be ordered if you have had abnormal Prothrombin Time (PT/INR) and Activated Partial Thromboplastin Time (aPTT) test results.

For your blood to clot, your body makes proteins known as coagulation (clotting) factors. These factors are activated one after the other in a step-by-step sequence, with each one playing a specific role in the clotting process. For normal clotting to occur, each factor must function properly and there must be enough of the factor for normal clotting to occur.

Fibrinogen is one of the final clotting factors in the process. Fibrinogen is changed into fibrin threads which form a mesh to create the blood clot and stop bleeding.

How blood clotting works

• Clotting is a normal part of healing. When you have an injury, and a blood vessel starts to bleed, your body triggers a series of interactions to make a blood clot to stop the bleeding.
• Platelets (thrombocytes) are tiny plate-shaped cells that circulate in your blood. When they sense damage to a blood vessel, they travel to the area where they change their shape by growing long tentacles, become sticky and clump together.
• When activated, platelets release chemicals to attract more platelets and other cells, setting off the next step. This is called the coagulation cascade.
• Clotting factors are activated one after the other.
• Fibrinogen is one of the final clotting factors. Your liver makes fibrinogen, and it circulates in your blood. When a clot is needed, it is converted into sticky fibrin threads which form a mesh that catches the platelets and holds them together.
• Once a clot is formed, other substances are activated to slow the clotting process. As the tissue heals and you don't need the clot anymore, the fibrin strands dissolve.
• Fibrinogen also helps start the inflammatory process by triggering the production of white blood cells. This is an important part of your immune response. Sometimes, fibrin can trigger more inflammation than is required.

A fibrinogen test is ordered when doctors want to check whether your blood can form a proper clot—especially if there is a suspicion of a bleeding or clotting problem, and/or if you have had abnormal PT/INR and aPTT test results.

Acquired conditions affecting fibrinogen

• Unexplained bleeding
  • Easy bruising
  • Frequent nosebleeds
  • Heavy menstrual bleeding
  • Bleeding after surgery or dental work
• Suspected clotting problems
  • As part of a coagulation screen (with PT/INR and aPTT)
  • When results from other clotting tests are abnormal
• Serious conditions affecting clotting
  • DIC – disseminated intravascular coagulation (fibrinogen is usually requested with other tests such as PT/INR, aPTT, platelets, fibrin degradation products (FDP) and D-dimer)
  • Severe infections or sepsis
  • Major trauma or burns
• Liver disease
  • The liver makes fibrinogen, so levels can fall if it’s not working properly
• Monitoring very unwell patients
  • In ICU, after major surgery, or during complications of pregnancy

Inherited conditions affecting fibrinogen

Several rare inherited disorders affect fibrinogen production. Dysfibrinogenaemia (abnormal fibrinogen production) is usually due to a rare mutation in the gene that produces fibrinogen. This causes the liver to make an abnormal fibrinogen. If your symptoms and health history findings suggest a fibrinogen problem, other specialised tests may be done to assess fibrinogen function further.

Two types of tests can be used to assess fibrinogen

• A fibrinogen activity test: This test finds out how well the fibrinogen process is working—not just how much of it you have. A chemical called thrombin is added to your blood sample. Thrombin turns fibrinogen into fibrin. The test measures the time it takes for a fibrin clot to form.
• A fibrinogen antigen test: This test measures how much fibrinogen is in your blood, regardless of whether it works properly. It uses antibodies that specifically stick to fibrinogen in your blood sample. These are detected as part of the test.

D-dimer and fibrinogen

Fibrinogen testing is often ordered along with a D-dimer test because they give complementary information about what’s happening in the clotting system:

• Fibrinogen tells you how much clotting ‘building material’ is available.
• D-dimer tells you whether clots are being broken down somewhere in the body.

Sample

Blood.

Any preparation?

Certain medications may affect your results. If you are taking medications discuss this with your doctor. These include anabolic steroids, androgens, phenobarbital, fibrinolytic drugs (streptokinase, urokinase, tPA) and sodium valproate. Moderate elevations in fibrinogen may also be seen with oral contraceptives or oestrogen treatment. Blood transfusions within the past month may also affect fibrinogen test results. Do not stop any medications unless your doctor advises you to.

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

Combined fibrinogen activity and fibrinogen antigen results

The fibrinogen activity test is usually ordered first, with the fibrinogen antigen test ordered as a follow-up test to see if lower activity is caused by insufficient fibrinogen or dysfunctional fibrinogen.

Fibrinogen testing on its own cannot usually make a diagnosis, but it provides useful information that, together with the results of other test results, can lead to a diagnosis.

Reference intervals - comparing your results to the healthy population

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people.
• They are used to provide a benchmark for interpreting a patient's test results.
• When compared against them, your results may be flagged high or low if they sit outside this range.
• Some reference intervals are harmonised or standardised, which means all labs in Australia use them.
• Others are not because for these tests, labs are using different instruments and chemical processes to analyse samples.
• Always compare your lab results to the reference interval provided on the same report.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation.

As different laboratories use varied reagents for testing of fibrinogen, differing fibrinogen results may be seen across laboratories. As reagents vary in their sensitivities to coagulation factors, it is important to check your specific laboratory’s ranges.

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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