How is haemophilia diagnosed?

Most people with haemophilia have a family history of the condition and so it will be suspected and diagnosed at or soon after birth. If there is no family history, which is the case for people who have the sporadic form of haemophilia due to new genetic mutations, diagnosis will not occur until bleeding problems develop. Diagnosis may also be delayed if the family is not aware that there is a family history- for example, if previous generations in the family have had only daughters who are carriers without symptoms or had sons who died in early childhood from undiagnosed haemophilia.

Severe haemophilia is usually diagnosed in the first year of life. People with mild or even moderate haemophilia may not be diagnosed for many years, even into adulthood, possibly discovering the condition as a complication of surgery.

Diagnosis is made using a series of blood tests to measure the level of clotting factor activity. If there is a known family history of haemophilia, genetic testing can be done during pregnancy. Genetic testing may also be performed to look at the genetic variant that is causing the haemophilia.