Reduced factor IX activity

What it means

Decreased activity of coagulation factor IX. Factor IX, which itself is activated by factor Xa or factor VIIa to form factor IXa, activates factor X into factor Xa.

Severe deficiency of factor IX underlies hemophilia B.

Rare diseases that can present with this3

The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.

Part of the broader category

Also called: Low factor IX activity