What Is Hemophilia?

Hemophilia (heem-a-FILL-ee-ah) is a rare inherited bleeding disorder. The blood does not clot normally. Persons with hemophilia may bleed for a longer time following an injury or accident than others. They also may bleed internally, especially in the joints (knees, ankles, and elbows).

Babies born with hemophilia are missing or have a low level of a protein needed for normal blood clotting or blood coagulation. The protein is called a clotting factor.

About 18,000 persons in the U.S. have hemophilia. About 400 babies are born each year with the disorder. Hemophilia usually occurs only in males (with very rare exceptions).

A person with hemophilia has a problem with certain proteins in the blood, called clotting factors, which help blood clot. Hemophilia can be due to:

• A low level of one of the clotting factors
  
  
• A clotting factor that is completely missing.

When clotting factors are missing, or your body does not have enough of these factors, it can take a long time for your blood to clot after an injury or accident.

What Is Clotting?

An injury (like a cut) to a blood vessel causes a complex chain of events that results in a blood clot. This is called the clotting process (also called blood coagulation). Clotting is your body's reaction to bleeding to keep you from losing too much blood. Losing too much blood can be life threatening and can damage your internal organs.

What Is a Clotting Factor?

Clotting factors are proteins in the blood that work with platelets--small blood cell fragments--to help the blood to clot. When blood vessels are damaged, clotting factors help the platelets stick together to plug cuts and breaks at the site of the injury.

In people with hemophilia, blood does not clot as it should due to missing or low levels of one of these clotting factors. If blood doesn't clot as quickly or as well as it should, then:

• Heavy blood loss can occur.
  
  
• Body organs and tissues can be injured.
  
  
• These conditions can result in permanent damage or death.

Sometimes people with hemophilia need infusions of clotting factor to stop bleeding.

Types of Hemophilia

There are two main types of hemophilia:

• Hemophilia A: Clotting factor 8 (VIII) is low or missing. About 9 out of 10 people with hemophilia have type A.
  
  
• Hemophilia B: Clotting factor 9 (IX) is low or missing.

Hemophilia also can be acquired when antibodies to these clotting factors form and block their function. Only inherited hemophilia is discussed here.

Hemophilia can be:

• Mild
• Moderate
• Severe.

This is determined by the amount of clotting factor in the blood. Most people (about 7 out of 10) with hemophilia A have the severe form. Normal persons have a factor 8 activity of 100 percent; persons with severe hemophilia A have less than 1 percent factor 8 activity.