Most bleeding disorders are inherited and affect people from all racial and ethnic groups. Although there are several different types, Hemophilia A, Hemophilia B and von Willebrand Disease are the most common.

Clotting factor tests are blood tests used to determine hemophilia type and severity. While those with severe hemophilia are in the majority, the severity of symptoms, bleeding patterns and key implications can vary greatly.

While factor level is one measure of bleeding risk, hemophilia phenotype is another. Some patients have factor levels that classify them as mild or moderate, but present with a severe bleeding phenotype (i.e. bleed more than expected based on factor levels).