Factor IX Activity

Factor IX (9) activity is a PTT-based factor assay used for diagnosing congenital factor IX deficiency (hemophilia B) and evaluating for acquired deficiencies associated with liver disease, vitamin K deficiency and factor IX inhibitors. Factor IX activity can also be used to monitor infusions of factor IX replacement therapy during procedures and prophylactic infusions.

Certain recombinant Factor IX formulations may give unreliable results with this assay, and chromogenic Factor IX activity assays should be used to monitor these patients.

Emicizumab (Hemlibra) will affect all PTT-based assays and will overestimate the factor concentration.

Outside clients should fill and submit Coagulation Patient Clinical History Form: Coagulation Patient Clinical History Form

Patients on bivalirudin (Angiomax), dabigatran (Pradaxa), rivaroxaban (Xarelto), apixaban (Eliquis), edoxaban (Savaysa) and argatroban (Novastan) may show prolonged clotting times. This may cause an under-estimation of the factor concentrations.

Emicizumab (Hemlibra) will affect all PTT-based assays and will overestimate the factor concentration.

Certain recombinant Factor IX formulations may give unreliable results with this assay, and chromogenic Factor IX activity assays should be used to monitor these patients.

Elevated factor VIII (8) levels (>250%) will result in a false increase in factor IX, XI, and XII assays.

UW-MT and HMC: Take specimen to Coag lab for processing.

Outside Laboratory: Centrifuge for 10 minutes, remove plasma & re-spin plasma for another 10 minutes. Decant & freeze plasma (minimum 1.0 mL) @ -20°C to -80°C. Send frozen on dry ice.