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Hemophilia: Let’s start with the basics.

What is hemophilia? How do people get it? And why? If you’ve got questions, we’ve got answers.

What is hemophilia?

To understand hemophilia, it’s helpful to know how the body normally works when it comes to stopping a bleed. When a person bleeds, 13 different proteins—called clotting factors—work together to form a blood clot.

In people living with hemophilia, one of the clotting factors is missing or reduced, which prevents this process from working. They have trouble forming blood clots—so it’s harder to stop bleeds when they happen.

Blood Drops Graphic

How do people get hemophilia?

People living with hemophilia are born with it. In the majority of these cases, it is passed to a child from the mother’s side of the family. Sometimes, a person may develop hemophilia without any family history. In fact, Nearly one-third of hemophilia cases are not inherited and have no family history of the disease.


All people who have hemophilia are diagnosed at birth.


Due to a lack of bleeding at birth or because the family doesn’t have a history of hemophilia, some people who have hemophilia are not diagnosed as newborns.


2 Types of Hemophilia Graphic

2 Types of Hemophilia

of people with hemophilia have hemophilia A. Also known as Factor VIII (8) deficiency, it is caused by a lack of the clotting factor known as Factor VIII.

of people with hemophilia have hemophilia B. Also called Factor IX (9) deficiency, it’s caused by a lack of—you guessed it—Factor IX. 


Mild, moderate, or severe hemophilia—what do they mean?


Mild Graphic

Mild hemophilia means a factor VIII or IX level ranging from 5% up to 40% of normal blood levels

Moderate Graphic

Moderate hemophilia refers to factor VIII or IX level ranging from 1% up to 5% of normal blood levels

Moderate Graphic

Severe hemophilia means a person has a factor VIII or IX level below 1% of normal blood levels


Hemophilia Fact

The spectrum of bleeding disorders.

Along with hemophilia A and B, 15 other bleeding disorders have been identified. What makes them different?

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