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Clotting; factor VIII, VW factor antigen

CPT4 code

Name of the Procedure:

Clotting; Factor VIII, VW Factor Antigen
Commonly known as: Factor VIII and Von Willebrand Factor (VWF) Assay


This procedure measures the levels of Factor VIII and Von Willebrand Factor in the blood. These are proteins involved in blood clotting, and their levels can help diagnose clotting disorders.


The procedure is used to diagnose bleeding disorders, such as Hemophilia A and Von Willebrand Disease. It helps determine if the blood has the proper ability to clot, which is crucial in preventing excessive bleeding.


  • Unexplained bruising or bleeding
  • Frequent nosebleeds
  • Heavy menstrual bleeding
  • Family history of bleeding disorders
  • Pre-surgical assessment for patients with suspected bleeding disorders


  • No specific preparation is typically required.
  • Inform the doctor of any medications or supplements you are taking, as some can affect clotting.
  • Fasting may be required in some cases.

Procedure Description

  1. A healthcare professional will draw a blood sample from a vein, usually in the arm.
  2. The sample is sent to a laboratory, where it is analyzed for the levels of Factor VIII and Von Willebrand Factor.
  3. The laboratory uses specific assays and reagents to measure the concentration of these clotting factors.
  4. No anesthesia or sedation is required.


The blood draw takes about 5-10 minutes. Laboratory results typically take several days.


The procedure is usually performed in an outpatient clinic, hospital, or laboratory setting.


Healthcare professionals involved include:

  • Phlebotomist or nurse for drawing the blood sample
  • Laboratory technician for analyzing the sample
  • Hematologist or primary care doctor for interpreting the results

Risks and Complications

  • Minor risks include bruising or discomfort at the blood draw site.
  • Rare risks might include infection or excessive bleeding.


  • Accurate diagnosis of bleeding disorders.
  • Guiding treatment and management of conditions like Hemophilia A and Von Willebrand Disease.
  • Results can help inform surgical and medical treatment plans.


  • Minimal to no recovery time is needed.
  • Patients can typically resume normal activities immediately.
  • Follow-up appointments may be scheduled to discuss results and treatment plans.


Other diagnostic tests for bleeding disorders include:

  • Complete Blood Count (CBC)
  • Prothrombin Time (PT) and Activated Partial Thromboplastin Time (aPTT) tests
  • Platelet function tests Each alternative has its own benefits and limitations; consult with a healthcare provider for the best choice.

Patient Experience

  • Mild discomfort or pain during the blood draw.
  • Minor bruising or soreness at the puncture site.
  • Overall, the procedure is quick and minimally invasive.
  • Pain management is typically unnecessary, but a cold pack can reduce any swelling or bruising post-procedure.

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