At what age is factor IX deficiency (FIX) (hemophilia B) typically diagnosed?

Updated: Mar 09, 2021
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: Srikanth Nagalla, MD, MS, FACP  more...
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Hemophilia B can be detected prenatally by measuring FIX activity in fetal blood samples obtained at 20 weeks of gestation by fetoscopy, but the presence of maternal FIX in amniotic fluid complicates the assessment. In addition, the procedure carries a high risk of complications, with a risk of fetal death of up to 6%. Detection of hemophilia B by linkage studies or gene mutation analysis (when the defect is known) can be performed by chorionic villous sampling at 12 weeks of gestation or by amniocentesis from 16-20 weeks, with complication rates of up to 2.0%.

Postnatal evaluation is triggered by a history of bleeding, which can start immediately after birth or, in mild hemophilia, can be delayed to a later age. Newborns without hemophilia have reduced levels of approximately 40%, with a gradual rise in the first year into the low-normal adult range. Prematurity is associated with lower levels due to the immaturity of the liver.

An age- and puberty-related (testosterone induced) rise in FIX levels, with an amelioration in bleeding symptoms, occurs in patients with FIX Leyden.

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