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Factor VIII (von Willebrand Factor) Activity or Concentration

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

This test measures the level of Factor VIII, a protein essential for blood clotting. Low levels can increase bleeding risk, while high levels may raise clot formation concerns.

Quick summary

["Factor VIII helps prevent excessive bleeding by aiding clot formation."]

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

Key facts at a glance

LOINC
3213-6
Short code
Fact VIII Ag PPP IA-aCnc
Synonyms
Fact VIII Ag PPP IA-aCnc
Category
chemistry
Sample
plasma
Container
Lavender-top (EDTA) or Green-top (Heparin)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ia
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 Is This Test Done?

Your doctor may order this test if you have a history of bleeding disorders, heavy menstrual bleeding, easy bruising, excessive bleeding after surgery or trauma, or if you’re considering a procedure that could cause bleeding. It’s also used to monitor treatment for bleeding disorders or von Willebrand disease.

What Does the Test Involve?

A blood sample is drawn from a vein, usually in your arm. The sample is processed to measure Factor VIII activity or concentration, often using an immunoassay or similar method. Results help assess your clotting ability.

What Are Common Results?

Results are typically reported as a percentage or ratio compared to a standard (e.g., 100% is normal). No specific numeric ranges are provided here, as they vary by lab and test type.

How Is This Test Different from Other Clotting Tests?

Unlike tests like PT (prothrombin time) or aPTT (activated partial thromboplastin time), which measure multiple clotting factors, Factor VIII tests specifically evaluate this protein’s role in clotting. It’s often used alongside other tests for a full picture of bleeding disorders.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Factor VIII Level

Frequently asked questions

Low Factor VIII levels may indicate von Willebrand disease or other bleeding disorders, increasing risk of prolonged bleeding. High levels could suggest clotting disorders or rare conditions. Regular monitoring is important if you’re on Factor VIII replacement therapy.
This test helps diagnose bleeding disorders, guides treatment decisions, and ensures proper management of Factor VIII replacement therapy if needed.
What does a low Factor VIII result mean?
A low result may mean you have a bleeding disorder, such as von Willebrand disease, or another condition affecting clotting. Your doctor may recommend further testing or treatment options, such as Factor VIII replacement therapy.
How often should I get this test?
Frequency depends on your medical condition. If you have a bleeding disorder, your doctor may order this test regularly to monitor your treatment effectiveness. If you’re healthy, it’s usually only done when symptoms or risk factors suggest it’s needed.
  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