How does the basal level of factor IX (FIX) correlate with the severity of bleeding in factor IX deficiency (FIX) (hemophilia B)?

Updated: Mar 09, 2021
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: Srikanth Nagalla, MD, MS, FACP  more...
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The relationship between the basal level of FIX and bleeding is shown in Table 1. Severity of bleeding correlates with the level of basal FIX activity.

Table 1. Correlation Between Severity of Bleeding and the Level of Basal FIX Activity (Open Table in a new window)


Functional FIX Levels, %

Bleeding and Hemarthroses


≤ 1

Lifelong spontaneous hemorrhages and hemarthroses starting in infancy



Hemorrhage secondary to minor trauma or surgery; occasional spontaneous hemarthrosis



Hemorrhage secondary to trauma, surgery, or precipitated by the use of drugs such as nonsteroidal anti-inflammatory drugs

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