Classification is based on plasma activity levels of factor IX.
Factor IX activity in plasma
Factor IX < 1% (< 1 U/dL)
Spontaneous bleeding, mainly in
1% (1 U/dl) <= Factor IX
Occasional spontaneous bleeding;
5% (5 U/dL) <= Factor IX
Serious bleeding in the event of trauma or surgery
Severe forms of hemophilia B are associated with the most serious hemorrhagic signs. These can appear after seemingly innocuous trauma that often go unnoticed and such episodes are thus referred to as spontaneous hemorrhages. There is a high risk of hemorrhage in the event of surgery.
Severe hemophilia B occurs in 30 to 40% of cases.
The most common hemorrhagic episodes consist of:
Gastrointestinal and central nervous system hemorrhagic accidents are potentially life-threatening, while others such as bleeding in the orbit, the front of the forearm or the axilla may compromise function. Emergency treatment is required at centers specializing in the treatment of hemophilia and involves administration of suitable products.