SEVERITY OF HEMOPHILIA The severity of hemophilia depends on how well or poorly the blood can clot. This is usually defined as mild, moderate, or severe. The more severe forms usually become apparent early on in life.17 Mild cases may go unnoticed until later, when unusual bleeding happens after surgery or an injury occurs. Whether the type is mild, moderate, or severe is assessed by measuring the level of clotting factor in the blood. Normal blood clotting  requires >30% of normal factor VIII and IX levels. Most hemophilia patients have levels <5%,17 the moderate or severe forms. Mild: People with mild hemophilia usually have factor levels of about 5% to 25% of normal. Problems with bleeding may occur only after serious injury, trauma, or surgery.17 In many cases, mild hemophilia is not discovered until an injury, surgery, or tooth extraction causes unusual bleeding. The first episode may not occur until adulthood. Moderate: People with moderate hemophilia have factor levels of about 1% to 5% of normal.17 Bleeding episodes tend to occur after injuries, but there may also be occasional bleeding episodes without obvious cause. These are called spontaneous bleeding episodes. Severe: People with severe hemophilia have a factor VIII or IX level <1% of normal.17 Bleeding usually begins soon after birth, and severe bleeding occurs throughout life, including bleeding episodes following injury, as well as frequent spontaneous bleeding episodes, often into the joints and muscles.