Factor IX activity

What it measures

Measures the activity of clotting factor IX. It diagnoses and grades hemophilia B and monitors factor IX replacement therapy.

Specimen and preparation

• Specimen: Citrated plasma (3.2% sodium citrate)
• Tube: Light_blue top
• Preparation: Process promptly or freeze plasma.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Pregnancy, oral contraceptives
• Inflammation

Causes of low values

• Hemophilia B (severe <1%, moderate 1–5%, mild 5–40%)
• Vitamin K deficiency or warfarin
• Liver disease
• DIC

Method

One-stage aPTT-based clotting assay or chromogenic assay

Good to know

Newborns normally have low vitamin K-dependent factors, so mild hemophilia B may need retesting at 6 months.

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