The Limitation of Factor IX Coagulant Activity Deter
mination in the Diagnosis of Hemophilia B Carriers
SARANYA RURGKHUM,B.Sc.*, WERASAK SASANAKUL, B.Sc.*,
SUKANY A CHOTSUPPAKARN, B.A.*, PAKAIMAS PINTADIT, B.Sc.*,
AMPAIWAN CHUANSUMRIT,M.D.**
Affiliation : * Research Center.
**Department of Pediatrics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand.
AbstractA preliminary study of factor IX coagulant activity (FIX:C) for determining hemophilia B
carriers was conducted at the Department of Pediatrics, Faculty of Medicine Ramathibodi Hospital
in Bangkok. Twenty-eight females (8 obligate, 20 potential carriers) from 17 hemophilia B families
were enrolled in the study. Additionally, 25 normal females were included. They were not pregnant
and not using oral contraceptives. Then, three cut-off levels of FIX:C including 50 per cent which
was the commonly used level; 57 per cent which was the mean-2 SD of normal females and 75 per
cent which was the level reported by Knobe and Ljung in 1999 were used for the diagnosis of hemo
philia B carriers. The sensitivities of these three cut-off levels were 12.5 per cent ( 118) for 50 per
cent, 37.5 per cent (3/8) for 57 per cent and 50 per cent (4/8) for 75 per cent. Also, the specificities
were 100 per cent (25/25) for both 50 and 57 per cent, and 96 per cent (24/25) for 75 per cent.
Although the low cut-off levels of 50 per cent and 57 per cent had low sensitivities, they yielded a
high specificity (100%) compared to the higher level of 75 per cent. In the present study, the sensi
tivity of the cut-off level at 75 per cent was much lower than that of the study by Knobe and Ljung
(93%) since the presented sample size of obligate carriers was rather small. So, enrollment of more
subjects should be further carried out. In conclusion, FIX:C determination alone showed a limitation
in the diagnosis of hemophilia B carriers. The addition of genetic analysis of linkage analysis or
mutation detection is required for a definite diagnosis.
Keywords : Hemophilia B, Carrier, Factor IX Coagulant Activity
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