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Clotting; factor VIII related antigen

CPT4 code

Name of the Procedure:

Clotting; Factor VIII Related Antigen Testing
Common name(s): Factor VIII Activity Test, FVIII Antigen Test
Medical term: Factor VIII: Ag Test


The Factor VIII Related Antigen Test is a blood test that measures the level of factor VIII related antigen, a protein essential for blood clotting. This test is commonly used to diagnose bleeding disorders like Hemophilia A.


Medical Condition:
  • Hemophilia A
  • Von Willebrand Disease
  • Other bleeding disorders
Goals/Expected Outcomes:
  • Identify deficient levels of factor VIII related antigen.
  • Confirm suspected diagnosis of a bleeding disorder.
  • Guide treatment plans to manage bleeding risks.


  • Unexplained prolonged bleeding
  • Frequent nosebleeds
  • Heavy menstrual periods
  • Family history of bleeding disorders
Patient Criteria:
  • Patients with a known family history of hemophilia or other clotting disorders.
  • Patients presenting with symptoms of excessive or unexplained bleeding.


Pre-procedure Instructions:
  • No specific fasting is generally required for this test.
  • Inform your healthcare provider about any medications you are taking, as some may affect blood clotting.
Diagnostic Tests/Assessments:
  • A complete blood count (CBC) may be ordered prior to the test to check overall health and other bleeding-related factors.

Procedure Description

  1. Blood Sample Collection:
    • A healthcare professional will apply a tourniquet to your arm to make veins more visible.
    • A clean area of your skin with an antiseptic where the needle will be inserted.
    • A blood sample is drawn from your vein using a needle and collected in a tube.
  2. Laboratory Analysis:
    • The blood sample is sent to a lab, where the level of factor VIII related antigen is measured using specific assays.
  • Tourniquet
  • Antiseptic swabs
  • Syringe and needle
  • Blood collection tubes
  • None required; only blood draw discomfort.


  • The blood draw itself takes about 5-10 minutes.
  • Lab results may take a few days to be processed and returned to your healthcare provider.


  • Performed in a hospital, outpatient clinic, or specialized laboratory.


  • Phlebotomist or nurse to draw blood
  • Laboratory technicians to analyze the blood sample
  • Hematologist or your primary healthcare provider to interpret results

Risks and Complications

Common Risks:
  • Minor bruising or bleeding at the needle site. ##### Rare Risks:
  • Infection at the needle site.
  • Fainting or dizziness during the blood draw.


  • Accurately diagnoses bleeding disorders.
  • Helps in creating an effective treatment plan.
  • Prevents complications from unmanaged bleeding disorders.


Post-procedure Care:
  • Apply pressure to the needle site to stop bleeding.
  • Keep the bandage on for a few hours.
Expected Recovery Time:
  • Immediate; no downtime required.
  • Keep the needle site clean and dry.
  • Avoid strenuous activities with the affected arm for a few hours.
Follow-up Appointments:
  • Your healthcare provider may schedule a follow-up to discuss test results and potential treatment plans.


  • Von Willebrand Factor Antigen Test: Another test for different bleeding disorders.
  • Factor IX Activity Test: Evaluates another clotting factor related to Hemophilia B.
  • Genetic testing: To identify specific mutations causing bleeding disorders.
Pros and Cons of Alternatives:
  • Alternatives may provide complementary or more detailed information.
  • Some alternatives may be more invasive or costly.

Patient Experience

During the Procedure:
  • You might feel a quick pinch or sting when the needle is inserted.
  • Some patients may feel light-headed or anxious about the blood draw.
After the Procedure:
  • Some minor discomfort or bruising at the site of needle insertion.
  • Pain can be managed with over-the-counter pain relievers if necessary.

By understanding the Factor VIII related antigen testing procedure, patients can be better prepared and informed about what to expect and how it can benefit their health care.

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