%0 Journal Article
%T Identifying hemophilia B carriers: Utility of aPTT, factor IX levels and ratios of factor IX to other Vitamin K dependent factors.
%A Shu M
%A Malcolmson C
%A Bosch A
%A Markovic T
%A Wakefield C
%A Bouskill V
%A Carcao M
%J Haemophilia
%V 30
%N 4
%D 2024 Jul 24
%M 38924261
%F 4.263
%R 10.1111/hae.15068
%X <B>BACKGROUND: </B>Diagnosing hemophilia B (HB) carrier status is important to manage bleeding in carriers and to prevent bleeding in potential offspring. Without a family history of hemophilia, diagnosing HB carrier status is challenging. Genetic testing is the gold-standard, however it is reserved for individuals with a high suspicion of carrier status.<BR><B>OBJECTIVE: </B>To describe the distribution of activated partial thromboplastin time (aPTT) and factor IX coagulant (FIX:C) levels in HB carriers and assess the ratio of FIX:C to other Vitamin K dependent factors (FII:C, FVII:C, FX:C) as an indicator of HB carrier status.<BR><B>METHODS: </B>In this retrospective, single-centre cohort study, subjects were included if they were obligate or genetically proven HB carriers. Distributions of aPTT and FIX:C were described and the relationship between FIX:C levels in carriers and severity of familial HB was analysed. Ratios of FIX:C to FII:C, FVII:C, FX:C were calculated.<BR><B>RESULTS: </B>Seventy-two female HB carriers (median age: 34 years; IQR 24-43) were included. Median aPTT and FIX:C levels were 33.0 s [IQR 30.0-37.0] and 57 IU/dL [IQR 43-74]. Fifteen carriers (21%) had mild HB (FIX:C levels of 10-40 IU/dL). FIX:C levels trended higher in carriers of mild HB versus carriers of moderate/severe HB. In six carriers, the median ratio of FIX:C to other Vitamin K dependent factors was 0.44, with 92% of ratios being ≤ 0.75.<BR><B>CONCLUSIONS: </B>aPTT and FIX:C levels were unreliable in diagnosing HB carrier status. A low ratio of FIX:C to other Vitamin K dependent factors may be a useful marker of HB carrier status.