Factor VIII Assay
This test measures factor VIII activity in the blood. It helps assess bleeding disorders, clotting risk and abnormal coagulation function.
Turnaround time
7 days
Biomarkers count
1
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Details about Factor VIII Assay
What is the Factor VIII Assay?
The Factor VIII Assay is a blood test that measures the activity of factor VIII, a crucial clotting protein involved in the coagulation cascade. Factor VIII works alongside other clotting factors to help blood clot properly after injury.
Abnormal factor VIII levels can lead to either excessive bleeding or increased clotting risk, depending on whether levels are low or elevated. The test is widely used in the investigation of inherited and acquired bleeding disorders, as well as thrombotic conditions.
This assay is a core investigation in coagulation and haematology practice.
Why do I need a Factor VIII test?
You may need this test if you have unexplained bleeding, bruising or a family history of haemophilia. Low factor VIII levels are characteristic of haemophilia A, while elevated levels are associated with increased risk of thrombosis.
The test is also used to monitor treatment response, assess clotting abnormalities and investigate prolonged clotting times seen on screening tests such as APTT.
Symptoms and scenarios where testing is recommended:
- Easy or excessive bruising
- Prolonged bleeding after injury or surgery
- Nosebleeds or heavy menstrual bleeding
- Family history of haemophilia
- Abnormal clotting test results
- Unexplained blood clots
- Monitoring clotting factor therapy
- Investigation of thrombosis risk
Benefits of the Factor VIII Assay
- Diagnoses haemophilia A
Essential for identifying factor VIII deficiency. - Assesses bleeding risk
Helps predict bleeding tendency. - Evaluates clotting risk
Elevated levels may indicate thrombosis risk. - Supports treatment monitoring
Used to assess response to factor replacement therapy. - Investigates abnormal clotting tests
Clarifies prolonged APTT findings. - Useful in inherited and acquired disorders
Applicable across multiple clinical scenarios. - Guides specialist referral
Supports haematology decision-making. - Clinically validated coagulation marker
Standard component of clotting assessment.
Step-by-Step: How Testing Works
Choose your preferred testing method
You can attend one of our UK partner clinics or arrange a home or hotel visit with a mobile phlebotomist.
Option 1 – In-Clinic Blood Draw
- Select your nearest UK clinic and book an appointment.
- A clinician or phlebotomist collects a venous blood sample.
- The sample is analysed for factor VIII activity.
- Results are delivered securely online.
Option 2 – Home or Hotel Phlebotomy (+£60)
- Book a UK-wide home or hotel visit at a convenient time.
- A trained phlebotomist collects your blood sample on-site.
- The sample is transported to the laboratory.
- Results are uploaded digitally without the need to travel.
Your Results Explained
Low Levels
Low factor VIII levels indicate impaired clotting ability.
This is commonly associated with haemophilia A or acquired factor VIII deficiency.
Typical UK reference range: ~50–150 IU/dL (ranges may vary by laboratory).
Normal Levels
Normal factor VIII activity suggests appropriate clotting function.
This reduces the likelihood of significant bleeding disorders related to factor VIII.
High Levels
Elevated factor VIII levels are associated with increased clotting risk.
This may contribute to venous thromboembolism and requires clinical correlation.
How It Works
Simple steps to get your results
Book Online
Choose your test online and book in seconds. Select your preferred clinic location or home visit option.
Visit or Test at Home
Attend one of our UK or London clinics, arrange a home nurse visit, or use a finger-prick kit where available.
Get Your Results
Your sample is analysed by accredited UK laboratories, with secure results delivered directly to you.
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WhatsApp UsHow to Prepare for Your Test
Follow these guidelines for accurate results
Sample Timing
Where possible, attend your blood test between 7am and 12pm. Please wait until any short-term illness or infection has fully resolved before testing. Avoid intense exercise for 24–48 hours beforehand, as this can affect certain markers.
Fasting & Hydration
Fasting is not always required, but some tests may recommend it. If fasting is advised, avoid food for 8–12 hours before your appointment and drink water only. Stay well hydrated, as this helps with sample collection and accuracy.
Medications & Supplements
Continue prescribed medications unless advised otherwise by your clinician. Avoid vitamin, mineral, or biotin supplements for at least 24–48 hours before your test, as these can interfere with results. If you are unsure about any medication or supplement, please let us know before your appointment.
Hormones & Menstrual Cycle
For hormone-related tests, timing within your menstrual cycle may be important. If relevant, follow any specific guidance provided on your test page.
If you have any questions or special circumstances, our team is happy to advise before your appointment.