Test Catalog

Test ID: FACR8    
Factor 8 Related Antigen Immunostain, Technical Component Only

Useful For Suggests clinical disorders or settings where the test may be helpful

Marker of endothelial cell lineage

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

For the initial technical component only immunohistochemical (IHC) stain performed, the appropriate bill-only test ID will be reflexed and charged (IHTOI). For each additional technical component only IHC stain performed, an additional bill-only test ID will be reflexed and charged (IHTOA).

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Factor 8-related antigen shows diffuse cytoplasmic staining of endothelial cells, megakaryocytes, and platelets. This immunostain may be used to support endothelial cell lineage in angiosarcoma.

Interpretation Provides information to assist in interpretation of the test results

This test does not include pathologist interpretation; only technical performance of the stain is performed. If an interpretation is required, order PATHC / Pathology Consultation for a full diagnostic evaluation or second opinion of the case.


The positive and negative controls are verified as showing appropriate immunoreactivity and documentation is retained at Mayo Clinic Rochester. If a control tissue is not included on the slide, a scanned image of the relevant quality control tissue is available upon request, call 855-516-8404.


Interpretation of this test should be performed in the context of the patient's clinical history and other diagnostic tests by a qualified pathologist.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Age of a cut paraffin section can affect immunoreactivity. Stability thresholds vary widely among published literature and are antigen-dependent. Best practice is for paraffin sections to be cut within 6 weeks.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Mak KM, Sehgal S, Harris CK: Factor VIII-related antigen detects phenotypic change of sinusoidal to vascular endothelium in hepatic fibrosis of elderly cadavers. Int Sch Res Notices. 2014 Sep 22;2014:839560. doi: 10.1155/2014/839560

2. Matino D, Gargaro M, Santagostino E, et al: IDO1 suppresses inhibitor development in hemophilia A treated with factor VIII. J Clin Invest. 2015;125(10):3766-3781. doi: 10.1172/JCI81859

3. de GrootJF, Fuller G, Kumar AJ, et al: Tumor invasion after treatment of glioblastoma with bevacizumab: radiographic and pathologic correlation in humans and mice. Neuro Onc. 2010 Mar;12(3):233-242