We hypothesize PK-guided dosing leads to individualization of prophylaxis which is in accordance with the recommendations of the subcommittee on FVIII, FIX, and rare bleeding disorders of the International Society on Thrombosis and Haemostasis (ISTH).37PK-guided dosing may help achieve higher trough levels more efficiently when clinically indicated, as well as provide guidance when patients switch to alternative replacement factor concentrates, while taking cost and benefit of treatment into account. Here, F8 is linked to hemorrhagic disease.