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Factor VIII Activity (Plasma)

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

This test measures the activity level of Factor VIII, a protein essential for blood clotting. Low levels can increase bleeding risk.

Quick summary

["Factor VIII helps your blood clot properly; low levels may raise your risk of excessive bleeding."]

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

Key facts at a glance

LOINC
38521-1
Short code
Fact VIII Ag Act/Nor PPP IA
Synonyms
Fact VIII Ag Act/Nor PPP IA
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, or unexplained bleeding. It’s also used to monitor treatment for hemophilia or von Willebrand disease.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into your arm or hand to draw blood. If you’re taking blood thinners, let your doctor know before testing.

What Happens During the Test?

Blood is collected in a tube and sent to a lab for analysis. The test checks how well Factor VIII helps your blood clot under controlled conditions.

What the Results Mean

Results are compared to a standard range. Very low levels may indicate bleeding disorders, while very high levels could be due to certain medications or conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Factor VIII is crucial for blood clotting. Deficiencies (like hemophilia) can cause severe bleeding, while excess may signal underlying conditions or medications.

Short name

Factor VIII Coagulation Factor

Frequently asked questions

Will I feel pain or discomfort?
You might feel a slight pinch or sting when the needle is inserted, but most people experience minimal discomfort. The area may bruise slightly afterward.
How long will it take to get my results?
Results are typically available within 1–3 business days, depending on lab processing times.
Can I eat or drink before the test?
You can eat and drink normally before the test, as it doesn’t affect blood collection.
  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