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  • Also Known As:
  • Serum Fibrinogen Test
  • Plasma Fibrinogen
  • Factor I
  • Factor 1 Assay
  • Hypofibrinogenemia Test
  • Fibrinogen Activity
  • Fibrinogen Antigen Test
  • Cardiac Fibrinogen
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Test Quick Guide

Fibrinogen testing is a group of tests that evaluate fibrinogen, one of several proteins in the body referred to as clotting factors. Clotting factors work together to form blood clots and stop bleeding when your body’s tissues or blood vessels are damaged.

Fibrinogen testing is used to evaluate and monitor people who have symptoms like excessive bleeding or abnormal blockages in veins or arteries. Doctors may diagnose a fibrinogen disorder, a type of blood clotting or coagulation disorder, if there is an issue with the amount of fibrinogen in the blood or with the ability of fibrinogen to form blood clots. A fibrinogen test may be ordered at the same time as a prothrombin time (PT) test and partial thromboplastin time (PTT) test, which are also used to assess the body’s ability to form blood clots.

About the Test

Purpose of the test

The purpose of a fibrinogen test is to evaluate the level of fibrinogen in the blood and to assess this protein’s ability to form blood clots. Fibrinogen testing can be used for diagnosing, monitoring, and screening for a number of conditions that affect blood clotting.

Diagnosing is evaluating a person to determine the cause of their symptoms. Measuring fibrinogen levels and assessing the ability of fibrinogen to form clots may be part of the diagnostic process for patients who experience excessive bleeding or constricted or blocked blood flow. Fibrinogen testing is usually performed after initial tests or examinations have ruled out other causes for these symptoms.

Monitoring is the process of periodically performing tests to assess the progression of a disease or a patient’s response to treatment. Obtaining a measurement of fibrinogen levels is routinely used in patients who are receiving fibrinogen replacement therapy after a diagnosis of a fibrinogen disorder.

Screening is testing to assess a patient’s risk of having a health problem before they develop symptoms. Fibrinogen testing may be ordered for some patients undergoing surgery to evaluate whether they are at a higher risk of excessive bleeding.

What does the test measure?

Fibrinogen testing measures the amount of fibrinogen and assesses whether a person’s fibrinogen is able to properly form blood clots.

Fibrinogen is a protein made in the liver that circulates in the blood. When injury occurs and bleeding needs to be stopped, fibrinogen works together with other clotting factors to form a blood clot, which is a mass of blood cells, platelets, and proteins that cluster together to stop bleeding.

During this process, which is also called coagulation, the body signals another clotting factor called thrombin to bind with fibrinogen. This process creates fibrin, a substance that builds a strong network of microscopic threads that strengthen the blood clot.

There are two methods for testing fibrinogen, which may be used simultaneously:

  • Fibrinogen antigen test: This test measures the amount of fibrinogen in a blood sample. It is generally reported in milligrams per decilitre (mg/dL).
  • Fibrinogen activity test: This test evaluates how much time it takes for fibrinogen to form a clot. For this test, thrombin is added to a prepared blood sample in order to stimulate the coagulation process in a test tube. The amount of fibrinogen that is incorporated into the blood clot is referred to as active fibrinogen and also reported in mg/dL.

When should I get a fibrinogen test?

Fibrinogen testing may be performed in situations where the blood’s clotting ability needs to be evaluated. It is usually prompted when a person has signs of abnormal blood clotting like excessive bleeding or a blockage of veins or arteries called thrombosis.

A health care provider may also order a fibrinogen test if the results of a prothrombin time (PT) or partial thromboplastin time (PTT) test indicate slow clotting times, even if a patient does not have symptoms.

Fibrinogen testing is ordered to evaluate or diagnose the following conditions:

  • Disseminated intravascular coagulation (DIC): DIC is a serious condition in which excessive amounts of thrombin and fibrin are produced by the body. Fibrinogen testing and other blood tests are needed to confirm a diagnosis of DIC.
  • Liver diseases: Fibrinogen and several other clotting factors are produced by the liver. Evaluating fibrinogen can assess the health of the liver and the risk of excessive bleeding in some patients.
  • Inherited fibrinogen disorders: Certain rare genetic conditions can cause changes in the production and function of fibrinogen that can lead to abnormal blood clotting. People with a personal or family history of fibrinogen disorders may have testing to confirm a diagnosis and plan treatment.
  • Other acquired fibrinogen disorders: Some types of cancer, autoimmune diseases, and certain medications can disrupt blood clotting. Fibrinogen testing can be used to evaluate how blood clotting is affected by these conditions.

Some people with fibrinogen disorders may undergo testing to assess their risk for abnormal bleeding or to plan treatment with supplemental fibrinogen replacement therapy. Routine fibrinogen testing is especially important in people who are pregnant and have a history of abnormal bleeding or previous pregnancy complications due to fibrinogen disorders.

Finding a Fibrinogen Test

How to get tested

Fibrinogen testing is ordered by a licensed health care professional. A blood draw is required and is usually conducted in a clinic, laboratory, or hospital.

Can I take the test at home?

A fibrinogen test can not be conducted at home. Unlike some other coagulation tests, fibrinogen testing can only be conducted in a laboratory with the appropriate equipment.

How much does the test cost?

The cost of fibrinogen testing depends on which type of test is ordered, where the test is performed, and whether you have health insurance coverage. While a person’s health insurance may cover the cost of testing, there may still be costs associated with a copay or deductible.

Check directly with your doctor or your insurance provider to learn about expected costs for fibrinogen testing.

Taking a Fibrinogen Test

Fibrinogen testing is usually performed after the results of other clotting factor tests indicate an abnormality that requires further evaluation. For a fibrinogen test, a blood draw is ordered by a health care provider and collected in a medical setting.

Before the test

No special preparation is required for a blood draw used for fibrinogen testing. In order to ensure the accuracy of the test, tell your doctor about any prescription or over-the-counter medications you are taking, especially anticoagulation medications that may affect the results of your fibrinogen levels.

During the test

For fibrinogen tests, a blood sample is taken with a needle inserted into a vein in your arm. There are a number of steps to a blood draw that you can expect:

  1. An alcohol wipe is used to disinfect your arm in the area where the needle will be inserted. This is most often on the inside of the elbow or the top part of the hand.
  2. A band called a tourniquet is then tied around your upper arm. The tourniquet increases blood pressure, making the vein in your arm more visible and easier to access with the needle.
  3. A needle is inserted in your vein. This may cause a pinch or a little pain. A separate tube is attached to the needle and filled with blood. Depending on the number of tests that are prescribed, there may be more than one tube of blood collected.
  4. After the test tubes are filled and the needle is removed the test is complete.

After the test

After the blood draw is complete, a bandage or cotton swab will be used to prevent bleeding. You may be instructed to keep this in place for an hour or more.

You may be able to return to normal activities, including driving, once the test is over, though it is common that the health care provider will have you stay for 15 minutes or so to observe you for any side effects. Bruising, dizziness, or lightheadedness are possible side effects after any blood draw, which may inhibit your ability to drive or walk.

You should contact your doctor if you notice any persistent pain, bleeding, or signs of infection following the test.

Fibrinogen Test Results

Receiving test results

Results of a fibrinogen test may be available within several business days of your blood sample arriving at the laboratory. You may receive a copy of your test results by mail or through an electronic health portal. Your doctor may also call you to discuss the test results or to schedule an appointment to review them together.

Interpreting test results

A report of your fibrinogen levels will show the amount of fibrinogen antigen and/or active fibrinogen in milligrams per deciliter (mg/dL), which will be compared to their reference range. Reference ranges, which can vary from lab to lab, help your doctor compare your fibrinogen level to the test results of a large sample of healthy people.

According to the American Board of Internal Medicine, the reference range for fibrinogen is 200-400 mg/dL. Reference ranges can vary depending on the procedures and equipment in each laboratory, so it is important to ask your doctor to help explain your test results.

The results of fibrinogen testing will generally be described as above, below, or within the reference range. However, fibrinogen levels are usually compared with other coagulation tests, like prothrombin time and partial thromboplastin time, in order to properly evaluate the severity and cause of abnormal blood clotting.

Abnormally low levels of fibrinogen can interfere with the creation of blood clots which may result in unexpected and excessive bleeding.

Fibrinogen disorders are associated with abnormal fibrinogen activity and low levels of fibrinogen. These disorders may be genetic, meaning they are inherited from a parent, or acquired as a result of injury or disease. Abnormal fibrinogen can be classified in the following ways:

  • Afibrinogenemia is a rare condition in which the body does not produce any functional fibrinogen.
  • Hypofibrinogenemia is a deficiency of fibrinogen, in which levels are chronically below 150 mg/dL.
  • Dysfibrinogenemia is a dysfunction of the fibrinogen, in which normal levels may occur, but the fibrinogen protein does not function normally.
  • Hypodysfibrinogenemia means that there is both a decrease in the amount of fibrinogen and its ability to form blood clots.

Abnormally high levels of fibrinogen may occur as part of the body’s normal response to an injury, infection, or inflammation. Higher levels of fibrinogen can also occur for the other reasons including:

  • Pregnancy
  • Aging
  • Tobacco use
  • Obesity
  • Insulin resistance

Higher levels of fibrinogen also increase the risk of experiencing a stroke or heart disease, though it is not known whether fibrinogen is a direct cause of these health problems.

The results of your fibrinogen test may be used to confirm a diagnosis or make a treatment plan. You should always review your fibrinogen test results with a health care provider who can help you understand how they apply to your personal health situation.

Are test results accurate?

Fibrinogen testing is generally considered accurate. However, there are some situations that can lead to abnormally low test results even when there is no underlying fibrinogen disorder.

Because fibrinogen is important for blood clotting, it is possible that handling or processing of a blood sample could stimulate clotting and affect a fibrinogen test result. Laboratory technicians take many steps to ensure safe handling of test samples, but if your fibrinogen test results are not what your doctor expected, they may order a repeat test.

Do I need follow-up tests?

Because there are multiple testing methods for measuring fibrinogen levels and activity, follow-up tests will depend upon which method was used and the initial purpose of testing. Confirmation of certain fibrinogen disorders may require that both a fibrinogen antigen and fibrinogen activity tests be performed.

Some fibrinogen disorders are hereditary, so patients may be referred to a health professional called a genetic counselor who can discuss whether genetic testing is appropriate to look for an inherited disorder.

Your health care provider can discuss whether follow-up testing is necessary for your situation.

Questions for your doctor about test results

When you review your fibrinogen test results, you may find it helpful to pose some of the following questions to your doctor:

  • What type of fibrinogen test did I have and what are the results?
  • Do my test results show that I have a condition that might be affecting my fibrinogen levels?
  • Do I need any follow-up tests based on my test result?

View Sources

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