Platform
Company
Coagulation
Review status
Currently under review
Pending specialist review and validation.
Factor VIII is a clotting protein that helps your blood form stable clots. This test measures how well factor VIII functions in your plasma using a standardized clot-based assay performed at a fixed dilution. It assesses activity, not just the amount of the protein.
Clinicians often order this test along with other coagulation studies, such as von Willebrand factor testing and screening tests like aPTT and PT, to understand your overall clotting health and pinpoint causes of bleeding or bruising.
Results help diagnose and manage conditions where factor VIII is too low, such as hemophilia A or an acquired inhibitor, which can lead to easy bruising, nosebleeds, heavy menstrual bleeding, or prolonged bleeding after procedures. The test also helps monitor responses to therapies like desmopressin or factor concentrates.
Higher activity can occur with inflammation, stress, pregnancy, or estrogen use and is linked with a higher tendency to develop blood clots in the veins. Your provider may check this result before surgery or dental work to plan bleeding prevention and tailor treatment to your situation.
Your provider will interpret your result together with your symptoms, medical history, medications, and other lab tests. A low result suggests reduced factor VIII function, which may be inherited or acquired, or may reflect low von Willebrand factor since that protein protects factor VIII. If the finding is unexpected, repeat testing when you are well and off short-term influences is often helpful.
A high result may be temporary due to inflammation, infection, stress, or hormones. If it remains high, your provider may discuss steps to reduce clotting risk and whether further evaluation is needed. Follow-up testing can include a mixing study, an inhibitor screen, a von Willebrand panel, or genetic testing, and plans will be individualized to your needs.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
This test uses a blue-top citrate tube that must be filled to the line and processed promptly. Underfilling or delayed centrifugation can falsely lower factor VIII activity.
Recent factor concentrates, desmopressin, estrogen or oral contraceptives, and some anticoagulants (including heparin contamination) can alter results. Tell your provider about all medicines and supplements.
Factor VIII behaves like an acute phase protein. Illness, infection, stress, or vigorous exercise can raise levels temporarily, so repeat testing in a stable state may be advised.
Pregnancy and estrogen therapy often increase factor VIII activity. Testing may be timed or repeated after delivery or after stopping hormones to understand your baseline.
Factor VIII is labile. Heat exposure, prolonged transport, or freeze-thaw issues can degrade activity and cause spuriously low results.
Severe liver disease, disseminated intravascular coagulation, or massive bleeding can change multiple clotting factors and complicate interpretation of factor VIII activity.
References