A collaborative Scientific and Standardization Committee project has redefined the categorization of hemophilia carriers (HCs). “The new nomenclature accounts for personal bleeding history, baseline [median plasma factor VIII/IX] FVIII/IX level, and distinguishes five clinically relevant HC categories to improve communication, harmonize clinical research, and allow adequate hemostatic management,” the researchers explained.

The 5 new categories for HCs and women/girls with hemophilia were defined as follows:

  • Severe, FVIII/IX < 0.01 IU/mL
  • Moderate, FVIII/IX 0.01 – 0.05 IU/mL
  • Mild, FVIII/IX >0.05 and <0.40 IU/mL
  • Symptomatic, normal factor levels (FVIII/IX > 0.40 IU/mL), with bleeding phenotype
  • Asymptomatic, normal factor levels (FVIII/IX > 0.40 IU/mL), without bleeding phenotype

The researchers reached a consensus after presenting the proposed new nomenclature at the meetings
of the Scientific and Standardization Committee on FVIII/IX & Rare Coagulation Disorder and Women’s Health Issues in Thrombosis and Hemostasis. The involved parties believe that this new nomenclature better reflects the HCs population.

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The basis of this redefinition was the misconception that female carriers tend to be asymptomatic. In fact, emerging evidence suggests an increased bleeding tendency in HCs, in spite of their FVIII/IX levels.

Hemophilia is a rare bleeding disorder that can affect both males and females. However, since hemophilia is inherited in an X-linked recessive pattern, it manifests in males more frequently.


Galen KPM, D’Oiron R, James P, et al. A new hemophilia carrier nomenclature to define hemophilia in women and girls: communication from the SSC of the ISTH. J Thromb Haemost. 2021;19(8):1883-1887. doi:10.1111/jth.15397