{"id":"factor-viii-activity","name":"Factor VIII Activity","shortName":"Factor VIII","aliases":["Factor VIII","Factor VIII:C","Factor VIII Assay","FVIII Activity","Antihemophilic Factor","Factor VIII Level","Factor VIII, One-Stage","Factor VIII, Activity","Coagulation Factor VIII Activity","Coag Factor VIII Activity Assay","Factor VIII Activity Assay","Chromogenic Factor VIII Activity","Factor VIII Activity, Chromogenic","Factor 8","Factor 8 Activity","FVIII:C","Antihemophilic Factor A"],"abbreviations":["FVIII","FVIII:C","F8"],"loinc":[{"code":"3209-4","primary":true},{"code":"3208-6","primary":false},{"code":"49865-9","primary":false},{"code":"3210-2","primary":false}],"specimen":"plasma","units":[{"ucum":"%","display":"%"},{"ucum":"[IU]/dL","display":"IU/dL"},{"ucum":"[IU]/mL","display":"IU/mL"}],"referenceRanges":[{"population":"Adults","low":55,"high":200,"unit":"%","unitDisplay":"%","note":"Adult interval from Mayo Clinic Laboratories (55–200% for the clot-based test, and the same for the chromogenic test). ARUP lists 56–191% for ages 18 and older. Mayo says full-term infants usually have at least 40%, and ARUP gives separate ranges for children. Factor VIII rises with inflammation, stress, hard exercise and pregnancy, and people with blood group O tend to run somewhat lower, so a result near either edge is often repeated. Many labs treat 1 IU/dL as 1% (WFH Table 2-1 lists them side by side), but the WFH laboratory chapter says IU/dL results are not strictly interchangeable with a percentage of a lab's own pooled plasma, so use the unit printed on your report.","sources":[{"title":"von Willebrand Disease Profile, Plasma (test AVWPR), including Coagulation Factor VIII Activity","url":"https://www.testcatalog.org/show/AVWPR","publisher":"Mayo Clinic Laboratories (Extended Catalog)"},{"title":"Chromogenic Factor VIII Activity Assay, Plasma (test CHF8)","url":"https://www.testcatalog.org/show/CHF8","publisher":"Mayo Clinic Laboratories (Extended Catalog)"},{"title":"Factor VIII, Activity (ARUP test 0030095)","url":"https://ltd.aruplab.com/Tests/Pub/0030095","publisher":"ARUP Laboratories"},{"title":"WFH Guidelines for the Management of Hemophilia, 3rd edition: Chapter 2, Comprehensive Care of Hemophilia (Table 2-1)","url":"https://www1.wfh.org/publications/files/pdf-1866.pdf","publisher":"World Federation of Hemophilia (Haemophilia)","year":2020},{"title":"WFH Guidelines for the Management of Hemophilia, 3rd edition: Chapter 3, Laboratory Diagnosis and Monitoring","url":"https://www1.wfh.org/publications/files/pdf-1867.pdf","publisher":"World Federation of Hemophilia (Haemophilia)","year":2020},{"title":"Thrombophilia testing: A British Society for Haematology guideline","url":"https://pubmed.ncbi.nlm.nih.gov/35645034/","publisher":"British Journal of Haematology","year":2022}]}],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"Measures how well factor VIII, a clotting protein that is low in hemophilia A, is working in your blood.","url":"https://bloodtesttracker.com/markers/factor-viii-activity","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}