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Factor VIII Activity (Plasma) – von Willebrand Factor-Related Activity

Published: August 9, 2026Updated: August 16, 2026

This test measures how much Factor VIII, a protein that helps blood clot, is present in your blood plasma. It helps diagnose bleeding disorders, including hemophilia A.

Quick summary

["Factor VIII activity helps identify bleeding risks and guide treatment for inherited clotting disorders."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
11911-5
Short code
GA from CRL.Hansmann85
Synonyms
GA from CRL.Hansmann85
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
1.5
Ref high
9
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
us-estimated-from-crl-hansmann
CPT
83002
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Matters

Factor VIII is a critical protein in the blood clotting process. Low levels can lead to excessive bleeding, especially after injuries or surgeries. This test is often used in patients with a family history of bleeding disorders or those who experience unexplained bruising, heavy menstrual bleeding, or prolonged bleeding from cuts.

How the Test Works

A small blood sample is drawn, and the plasma is tested to measure Factor VIII’s ability to help blood clot. The result is expressed as a percentage of a normal value, helping doctors determine if treatment is needed.

Common Reasons for Testing

Doctors may order this test if you have symptoms like frequent bruising, nosebleeds, heavy periods, or bleeding after dental work. It’s also used in newborn screening for hemophilia A or before surgeries to assess bleeding risk.

What to Expect Before the Test

No special preparation is needed, but avoid aspirin or other blood thinners for at least 48 hours before testing, as they can affect clotting.

Reference range

Follicular: 1.5-9.0 mIU/mLN/A

Specimen: serum

For females: inform if menstrual cycle status. For certain tests, timing within menstrual cycle may matter.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Factor VIII Activity

Frequently asked questions

What does a low or high result mean?
Low Factor VIII activity (below normal) strongly suggests a bleeding disorder like hemophilia A. High levels may indicate liver disease or other conditions affecting protein production.
How long does it take to get results?
Results are typically available within 24 to 48 hours, depending on lab processing times. Follow-up with your healthcare provider to discuss next steps if needed.
Can lifestyle changes affect this test?
While diet and exercise generally don’t directly impact Factor VIII levels, avoiding blood-thinning medications is critical. Always check with your doctor before making changes.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy