Factor VIII activity

Clotting · also printed as FVIII, Factor 8, Factor VIII, Factor VIII:C, F8 activity

Typical UK adult range50 to 150 IU/dL

Ranges vary between laboratories; the range printed on the report takes precedence.

What this test measures

Factor VIII is one of the clotting proteins. Low levels cause haemophilia A; high levels are seen with inflammation and are linked with clotting tendency.

Why doctors request it

Requested in bleeding disorders, alongside von Willebrand testing, and sometimes after unexplained clots.

What commonly pushes it up

Inflammation, pregnancy, oestrogen and stress
Some inherited patterns

What commonly pushes it down

Haemophilia A, inherited, or a carrier state
Von Willebrand disease
Acquired antibodies against factor VIII, rarely

Everyday reasons for a value outside the range

It is an acute-phase protein, so infection and stress raise it

About the sample

Best taken when well.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.

Got a report with Factor VIII activity on it?

Upload a photo or PDF and see every line against the range your lab printed, explained in plain English. First report free.

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This is an educational summary of results you uploaded. It is not medical advice, a diagnosis or a treatment plan, and it does not replace the doctor who requested the test. If you are worried, or a result is marked outside range, discuss it with your doctor. Written and reviewed by a UK consultant physician. Reference ranges vary between laboratories.