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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 in your blood that helps prevent bleeding by working with Factor IX to form a clot.

Quick summary

["Factor VIII helps control bleeding; low levels may increase risk of bleeding disorders."]

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

Key facts at a glance

LOINC
10521-3
Short code
Fact VIII Ag Tiss Ql ImStn
Synonyms
Fact VIII Ag Tiss Ql ImStn
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
immune-stain
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 Is Done

Your doctor may order this test if you have symptoms of bleeding, such as easy bruising, prolonged bleeding from cuts, or unexplained nosebleeds. It may also be done before surgery to ensure your blood clotting is stable, or if you have a known bleeding disorder like hemophilia.

What to Expect Before the Test

A blood sample is taken from a vein in your arm. You may feel a brief pinch when the needle is inserted, but the procedure usually takes less than five minutes. No special preparation is needed, but inform your doctor about any medications you’re taking, especially blood thinners.

What the Results Mean

Results are typically reported as a percentage of normal activity. A lower than normal level may indicate a bleeding disorder, while higher levels may be seen in certain medical conditions or after blood transfusions. Your doctor will interpret results in the context of your symptoms and medical history.

Common Conditions Affecting Results

Low Factor VIII levels can be caused by inherited bleeding disorders (e.g., hemophilia A), liver disease, or certain medications. High levels may occur in conditions like von Willebrand disease or after blood transfusions. Chronic liver disease or autoimmune disorders can also influence results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Factor VIII Level

Frequently asked questions

How often will I need this test?
If you have a known bleeding disorder, your doctor may schedule regular monitoring to track your Factor VIII levels. For routine screening or pre-surgery checks, results may be reviewed only once or twice a year, depending on your condition.
Can I eat or drink before this test?
No special diet is required for this test. You can eat and drink normally, but avoid alcohol for at least 24 hours before the test if possible, as it may affect blood clotting.
Will I need to take any special precautions after the test?
After the blood draw, apply gentle pressure to the site to stop bleeding. Avoid vigorous activity for a few hours. If you experience excessive bruising or bleeding, contact your doctor immediately.
  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