Factor VIII activity

What it measures

Measures the activity of clotting factor VIII. It diagnoses and grades hemophilia A, helps evaluate von Willebrand disease and monitors factor replacement.

Specimen and preparation

• Specimen: Citrated plasma (3.2% sodium citrate)
• Tube: Light_blue top
• Preparation: Process within 2 h or freeze plasma. Stress, exercise and pregnancy raise levels.

Reference range

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

Causes of high values

• Acute phase response (inflammation, surgery)
• Pregnancy, estrogen therapy
• Stress and exercise
• Associated with increased thrombosis risk

Causes of low values

• Hemophilia A (severe <1%, moderate 1–5%, mild 5–40%)
• von Willebrand disease
• Acquired hemophilia (factor VIII inhibitor)
• DIC

Method

One-stage aPTT-based clotting assay or chromogenic assay

Good to know

If factor VIII is low without family history, test for an inhibitor (Bethesda assay) and check vWF.

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