Which two proteins serve as markers for CSF?

• A. transthyretin and tau
• B. albumin and immunoglobulin
• C. transferrin and ceruloplasmin
• D. alpha-fetoprotein and beta-2 microglobulin

Answer: (A)

Understanding cerebrospinal fluid (CSF) biomarkers hinges on recognizing proteins that are characteristic of CSF itself and related to neural health. Tau is a neuron-derived protein that ends up in the CSF when neurons are damaged or undergoing degeneration; measuring CSF tau levels provides information about neurodegenerative processes and disease activity. Transthyretin is a transport protein produced by the choroid plexus and present in high amounts in CSF, reflecting the protein makeup of the CSF compartment. Together, these two proteins are closely tied to CSF origin and neural pathology, making them a natural pairing as CSF markers.

Other protein groups listed are not as specifically tied to CSF identity or neurodegenerative signaling. Albumin and immunoglobulin are primarily used to assess blood–CSF barrier function and CSF contamination from plasma rather than to define CSF itself or indicate neural disease in a direct way. The remaining pairs include proteins that are less characteristic as standard CSF markers in routine practice or pertain to other clinical contexts.