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Clinical severity of haemophilia A: does the classification of the 1950s still stand?

Summary.  The classification of haemophilia originates from 1950s and has been adopted unchallengedly by the ISTH in 2001. The aim of this study was: does the current classification compare onset of bleeding and age at first treatment, as well as annual joint bleeding frequency according to baseline FVIII activity? Data on age and reason of diagnosis, onset of treatment, onset of bleeding and bleeding frequency from 411 patients with haemophilia A born after 1970 were collected. Data were analysed according to base‐line FVIII activity levels. Age at diagnosis, onset of bleeding and start of treatment according to FVIII activity were compared with the current classification. Overall, the distinction between severe and non‐severe haemophilia was clear. The distinction between mild and moderate haemophilia was more difficult, mostly due to the wide variability in the group of patients with moderate haemophilia. Patients with severe haemophilia experienced their milestones like diagnosis, first treatment and joint bleed earliest, mostly as infants aged 0–3 years, whereas patients with moderate haemophilia reached these milestones around toddler age, 2–7 years, and patients with mild haemophilia reached them when they were in elementary school, around the ages of 5–14 years. This study confirms the clinical distinction between severe and non‐severe haemophilia A. However, the group of moderate haemophilia patients showed a wide variability, warranting close follow‐up and individualized treatment.