The limitation of factor IX coagulant activity determination in the diagnosis of hemophilia B carriers.
A 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 hemophilia B carriers. The sensitivities of these three cut-off levels were 12.5 per cent (1/8) 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 sensitivity 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.
Rurgkhum
Saranya
S
Research Center, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand.
Sasanakul
Werasak
W
Chotsuppakarn
Sukanya
S
Pintadit
Pakaimas
P
Chuansumrit
Ampaiwan
A
D000293:Adolescent; D000328:Adult; D005164:Factor IX / Q000032:analysis*; D005260:Female; D002836:Hemophilia B / Q000097:blood*; D006579:Heterozygote; D006801:Humans; D008875:Middle Aged; D012680:Sensitivity and Specificity
D005164:Factor IX