Severity levels
of hemophilia B

While mild hemophilia B is the most common level of severity, there are three forms: mild, moderate, and severe.

MY HOME Hemophilia B Severity Levels

From mild to severe hemophilia B1

In hemophilia B, clotting factor IX is either deficient or completely missing. The severity of hemophilia B is related to the amount of clotting factor IX you have.

The standard factor IX level is 100%. You can have a factor IX level between 50% and 150% and still be considered normal. In a person with hemophilia B, the clotting factor IX level is much lower than the standard.

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What are the 3 severity levels of hemophilia B?

Your level of hemophilia B is determined by the amount of working factor IX in your blood.1

6 to 49 percent icon.

Mild

Factor IX levels of 6-49%

1 to 5 percent icon.

Moderate

Factor IX levels of 1-5%

Less than 1 percent icon.

Severe

Factor IX levels of less than 1%

Patients with severe hemophilia B are usually diagnosed around birth or within the first years of life, while mild hemophilia B may not be diagnosed until later in life—or even on into adulthood.2

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  1. National Hemophilia Foundation. Hemophilia B. https://www.hemophilia.org/bleeding-disorders-a-z/types/hemophilia-b. Accessed February 13, 2023.
  2. Centers for Disease Control and Prevention. Diagnosis of hemophilia. https://www.cdc.gov/ncbddd/hemophilia/diagnosis.html. Accessed February 13, 2023.
  3. Hemophilia of Georgia. Severity levels. von Willebrand Disease & Platelet Disorders Handbook. 2023. https://www.hog.org/handbook. Accessed February 13, 2023.