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

1. Select your nearest UK clinic and book an appointment.
2. A clinician or phlebotomist collects a venous blood sample.
3. The sample is analysed for factor VIII activity.
4. Results are delivered securely online.

Option 2 – Home or Hotel Phlebotomy (+£60)

1. Book a UK-wide home or hotel visit at a convenient time.
2. A trained phlebotomist collects your blood sample on-site.
3. The sample is transported to the laboratory.
4. 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.