Jeannie Williams, a laboratory technician at Memorial Hospital in Springfield, IL, posed a question about beta-2 transferrin testing on cerebrospinal fluid (CSF). Because beta-2 transferrin is a normal constituent of CSF, but not of plasma or mucosal secretions, it is useful in determining whether a patient's nose or ear is leaking CSF versus some other fluid. This is important in determining whether an occult skull fracture or defect has opened a potential route of infection into the central nervous system. In addition to the CSF, beta-2 transferrin is present in the occular humors and the inner ear fluid, which could be an alternative source of this protein in trauma cases where the central nervous system is not actually breached. Beta-2 transferrin is alternatively known as tau protein (the same tau, in a hyperphosphorylated form, which makes up the tangles of Alzheimer disease). Beta-2 transferin is a type of microtubule-associated protein (MAP), which is a protein that binds and regulates the stability of cytoskeletal filaments. In the hospital laboratory, beta-2 transferrin can be detected electrophoretically by immunofixation. Thanks for the question, Jeannie!
Sources: Tietz Clinical Guide to Laboratory Tests, 4th Edition, Alan H.B. Wu (editor), Saunders Elsevier 2006, p. 1063-5. Molecular Biology of the Cell, 4th Edition, Bruce Alberts, et al. (editors), Garland Science 2002, p. 935.