F8 and obstructive sleep apnea syndrome: Preliminary FVIII antigen data correlate with CSA-determined FVIII:C,153 whereas preliminary phenotypic data supporting OSA-determined FVIII:C correlate with hepatocyte-derived FVIII in vivo function,152 suggesting that hepatocyte-derived FVIII may be more easily converted from its procofactor to cofactor state.