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Factor IX Assay

What is a Factor IV Assay Test?

Your doctor may recommend a factor IX assay test to determine if your body produces a healthy level of this particular coagulation factor. Your body needs this factor in order to form blood clots.

Each time you bleed, a series of reactions known as the coagulation cascade is triggered. Coagulation is the process your body uses to stop blood loss. Cells called platelets create a plug to cover the damaged tissue and then your body’s 13 clotting factors interact to produce a firm blood clot. Low levels of clotting factors can prevent a clot from forming.

What the Test Addresses

Your doctor will usually order a factor IX assay to determine the cause of prolonged or excessive bleeding. If you have a bleeding issue, see your doctor immediately.

Your doctor may order this test if a member of your family suffers from inherited factor IX deficiency, also known as hemophilia B. This disorder affects one in 30,000 males. This hereditary condition only affects males because it is linked to a defective gene on the X chromosome. Females have two X chromosomes, so if one has a defective gene, the other can still create enough factor IX.

The test may also be used to determine if you have acquired factor IX deficiency, which is often linked to vitamin K deficiency, liver disease, or the use of blood-thinning medications.

Your doctor may also recommend this test if you are male and you experience any of the following symptoms:

  • blood in your urine or stool
  • excessive bruising
  • frequent nosebleeds
  • bleeding in the digestive tract
  • bleeding in the urinary tract
  • prolonged bleeding from cuts, dental procedures, or surgery
  • spontaneous bleeding

Preparation for the Test

No special preparation is necessary for this test. You should tell your doctor if you are taking any blood-thinning medications, such as warfarin (Coumadin). Your doctor will advise you to stop taking blood thinners before the test.

How Is the Test Administered

To perform the test, your doctor will need to take a sample of blood from your arm. First the site will be cleaned with an alcohol swab. Then, the doctor will insert a needle into your vein and attach a tube to the needle to collect blood. When enough blood has been collected, the needle will be removed and the site covered with a gauze pad. The blood sample will be sent to a laboratory for analysis.

Understanding Your Test Results

Normal Results

A normal result for a factor IX assay should be between 50 and 200 percent of the laboratory reference value. Your doctor will explain the specifics of your results.

Abnormal Results

If your results are abnormal, it means that you have a low level of factor IX. This could be caused by:

  • inherited factor IX deficiency (hemophilia B)
  • disseminated intravascular coagulation (a disease in which blood clotting proteins are over-active)
  • vitamin K deficiency
  • poor fat absorption
  • use of blood-thinning drugs

What Are the Risks of the Test?

As with any blood test, there is a slight risk of bruising or bleeding at the puncture site. In rare cases, the vein may become swollen after blood is drawn. Applying a warm compress several times a day can treat this condition, known as phlebitis.

Ongoing bleeding could be a problem if you suffer from a bleeding disorder or are taking blood-thinning medication, such as warfarin or aspirin.

What to Expect After the Test

A factor IX deficiency can be treated with a fresh frozen plasma transfusion or injection of factor IX concentrate. How much substitute factor IX you need will depend on:

  • the frequency and severity of bleeding episodes
  • the location of the bleeding
  • your age, weight, and height

You doctor may teach you and your family members to use factor IX concentrates at home to prevent an emergency. They should be used at the first sign of bleeding. If you have severe hemophilia, you may also need ongoing plasma infusions and injections of concentrate before surgery or dental procedures.

You should also get a hepatitis B vaccine because, if you suffer from hemophilia, you are at a greater risk of contracting hepatitis from receiving blood transfusions or injections.

Content licensed from:

Written by: Corinna Underwood
Medically reviewed : George Krucik, MD

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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