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 haemophilia B are associated with the most serious haemorrhagic signs. These can appear after seemingly innocuous trauma that often go unnoticed and such episodes are thus referred to as spontaneous haemorrhages. There is a high risk of haemorrhage in the event of surgery.
Severe haemophilia B occurs in 30 to 40% of cases.
The most common haemorrhagic episodes consist of:
Gastrointestinal and central nervous system haemorrhagic 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 centres specialising in the treatment of haemophilia and involves administration of suitable products.