Clotting Factor IX (Christmas Factor) Activity in Platelet-Poor Plasma by Chromogenic or Clotting-Based Assay

What This Test Measures

Factor IX, also called Christmas factor, is a protein made mainly in the liver that works in the coagulation cascade. This test measures the activity level of factor IX in plasma, the liquid part of blood after cells and platelets have been removed. Activity is usually reported as a percentage compared with a normal reference standard.

Why Doctors Order It

Doctors may order a factor IX activity test when a person has unusual or prolonged bleeding, a family history of a bleeding disorder, or abnormal results on routine clotting tests such as a prolonged aPTT. It is also used to monitor people known to have hemophilia B or other factor IX deficiencies.

How the Sample Is Collected

A blood sample is drawn from a vein and collected in a tube containing an anticoagulant. The sample is then processed in the laboratory to separate platelet-poor plasma, which is the specimen used for this test. Proper collection and handling are important because clotting factors can degrade if the sample is not processed correctly.

What the Results Mean

Results are usually reported as a percentage of normal factor IX activity. A low result can suggest a factor IX deficiency, which may be inherited (such as hemophilia B) or acquired. A normal result generally means factor IX activity is within the expected range. Your doctor will interpret the result along with your symptoms, family history, and other clotting tests.