Severity levels
of hemophilia B

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

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.

Mother playing with her daughter.

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.


Factor IX levels of 6-49%

1 to 5 percent icon.


Factor IX levels of 1-5%

Less than 1 percent icon.


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

Keep exploring

Doctor consulting the patient.

How is hemophilia B diagnosed?

Pharmacist organizing drawer with medications.

Treatment options for hemophilia B

Man reading a book.

Connect with a Community Education Specialist

  1. National Hemophilia Foundation. Hemophilia B. Accessed February 13, 2023.
  2. Centers for Disease Control and Prevention. Diagnosis of hemophilia. Accessed February 13, 2023.
  3. Hemophilia of Georgia. Severity levels. von Willebrand Disease & Platelet Disorders Handbook. 2023. Accessed February 13, 2023.