Why is this marker being tested?
A factor VIII activity blood test lets doctors evaluate the functioning of a protein that helps blood to clot.
What is a clot?
A clot is a lump of blood that the body produces to prevent excessive bleeding by sealing leaks from blood vessels caused by wounds, cuts, scratches, or other conditions.
What is blood clotting and what are clotting factors?
Blood clotting is a process involving platelets (also called thrombocytes) and proteins called clotting factors. Platelets are oval-shaped cells made in the bone marrow. Most clotting factors are made in the liver. When a blood vessel breaks, platelets are first to the area to help seal the leak and temporarily stop or slow bleeding. But for the clot to become strong and stable, the action of clotting factors is required.
How are clotting factors numbered?
The body's clotting factors are numbered using the Roman numerals I through XII. They work together in a specialized sequence, almost like pieces of a puzzle. When the last piece is in place, the clot develops — but if even one piece is missing or defective, the puzzle can't come together.
Where is Factor VIII involved in the blood clotting process?
Factor VIII, with factor IX, is involved in the last step of the clotting process — the creation of a "net" that closes a torn blood vessel.
What is hemophilia A?
Under normal circumstances, certain proteins, including factor VIII, come together to form blood clots and quickly stop bleeding.
When an abnormal gene causes a person to be deficient in factor VIII, the result is a bleeding disorder known as hemophilia A. A factor IX deficiency is known as hemophilia B. Both conditions are usually hereditary, but also can occur spontaneously. Hemophilia A is the most common severe bleeding disorder. In hemophilia A, blood doesn't clot as it should. This puts a person at risk of uncontrolled bleeding.
Note: Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you.
Test results are usually reported as a percentage of a "normal" result of 100%. Normal ranges for factor VIII levels are 50% to 150%.
If your factor VIII protein levels are low, you may have hemophilia A. Almost all people with hemophilia A are male. Women are generally only carriers of the gene and have a 50% chance of passing it on to each of their children. (Boys who receive the gene would be affected and girls would be carriers). But it's possible for females to develop mild symptoms of this disorder.
You may need this test if you have a family history of the disorder or if you have one or more of these symptoms:
- Prolonged and unexplained bleeding after minor cuts, surgeries, or dental procedures
- Easy bruising
- Slow wound healing because of repeated bleeding or infection
- Joint pain and stiffness
- Swollen, hot joints or deformities
- Heavy menstruation
- Severe low back pain, usually on one side
- The need for a blood transfusion after a minor injury
You may also have this test if you have abnormal results from other blood tests that measure how well your blood clots.
Decreased Factor VIII Activity may be due to:
- Hemophilia A (a bleeding disorder caused by a lack of blood clotting factor VIII)
- Disorder in which the proteins that control blood clotting become overactive disseminated intravascular coagulation (DIC)
- Presence of a Factor VIII inhibitor (antibody)
- Von Willebrand disease (another type of bleeding disorder)
Increased Factor VIII Activity may be due to:
- Older age
- Liver disease
Factor VIII levels are elevated at birth and increase during pregnancy. Factor VIII is an acute phase reactant with levels that rise during periods of acute stress, following surgery, and in inflammatory conditions. Levels can also increase as the result of strenuous exercise or the administration of several drugs including epinephrine, DDAVP, or estrogen (for birth control or hormone replacement therapy). Factor VIII levels can be elevated in a number of clinical conditions including carcinoma, leukemia, liver disease, renal disease, hemolytic anemia, diabetes mellitus, deep vein thrombosis, and myocardial infarction.
Persistent elevation of factor VIII above 150% is associated with an increased risk for venous thrombosis of more than fivefold. Elevated factor VIII is also associated with an increased risk for recurrence of venous thromboembolism. Risk is graded such that the higher the factor VIII activity, the higher the risk. The basis for this increased risk is not well understood as genetic studies of the factor VIII and von Willebrand factor genes failed to identify a genetic basis for this increased risk. Values >150% are observed in 20% to 25% of individuals with venous thrombosis or thromboembolism in the absence of other known causes of factor VIII elevation.
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