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Factor VIII Activity (Plasma)

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.

Quick summary

["Factor VIII helps control bleeding; low levels may indicate bleeding disorders."]

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

Key facts at a glance

LOINC
51889-4
Short code
Num units trans Fact VIII
Synonyms
Num units trans Fact VIII
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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

What Does Factor VIII Measure?

Factor VIII is a clotting factor produced by the liver. It works with Factor IX to activate Factor X, which is crucial for forming blood clots. Deficiencies in Factor VIII can lead to hemophilia, a genetic condition causing excessive bleeding.

Why Is This Test Done?

Doctors may order this test to diagnose or monitor bleeding disorders, evaluate symptoms like excessive bruising or bleeding after injuries, or assess patients with known Factor VIII deficiencies.

When Might You Need This Test?

You might need this test if you have symptoms like frequent nosebleeds, easy bruising, prolonged bleeding from cuts, or joint bleeding. It’s also used before surgeries or dental procedures to ensure safe clotting function.

What to Expect Before the Test

No special preparation is needed. Blood is drawn from a vein, usually in your arm. You may feel a brief pinch, but it’s quick and painless. Avoid heavy exercise or aspirin-based medications for 48 hours before testing if instructed.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Low Factor VIII levels can lead to hemophilia or von Willebrand disease, increasing bleeding risk. High levels may be seen in certain liver diseases or after blood transfusions. Regular monitoring helps manage clotting disorders effectively.

Short name

VIII Activity

Frequently asked questions

How long does it take to get results?
Results are typically available within 1–3 business days, depending on lab processing times. Your healthcare provider will discuss findings with you.
What does a low Factor VIII level mean?
A low level suggests a potential bleeding disorder. Your doctor may recommend further testing or treatment options, such as clotting factor replacement therapy.
Can lifestyle changes affect Factor VIII levels?
While diet and exercise generally don’t directly alter Factor VIII levels, avoiding medications that thin blood (like aspirin) can help prevent excessive bleeding if you have a deficiency.
  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