To diagnose haemophilia, a cord blood sample from the newborn baby can be used. This applies to mild, moderate and severe cases. In at least 30% of cases of haemophilia there is no known family history and the occurrence of haemophilia is presumed to be the result of a spontaneous genetic mutation.

Cases of severe haemophilia may become apparent and be diagnosed at an early age as a result of surgery or injury. For example, prolonged bleedings may follow circumcision, routine blood sampling or routine childhood vaccinations.

More often the first symptom of a bleeding tendency is in the form of extensive bruising as the child learns to crawl or walk. Unfortunately this is sometimes suspected to be a result of non accidental injury, but increasingly in such cases it is automatic that coagulation tests are used to investigate the possibility of a child having a bleeding disorder. Cutting teeth is another stage at which the condition may become apparent.

Moderate and mild haemophilia may not be diagnosed until later in childhood or in some cases even in adulthood. Because there is some clotting factor available, more minor injuries will heal normally and it may not be until a major injury occurs that the deficiency is revealed.

The process of diagnosis involves many complex laboratory tests on blood samples and takes several days to complete. The time around diagnosis can be a difficult period for families.