Haemophilia Severity Classification

While laboratory thresholds are standard, some patients with < 1% activity have a "moderate" clinical phenotype, while others with 2-3% activity bleed spontaneously like "severe" patients. Clinical phenotype should ultimately guide prophylaxis decisions.

These thresholds have been the foundation of haemophilia care since the 1950s, refined by the ISTH in 2001 to ensure uniform language in global clinical trials.