Targeted Absolute Quantification of Protein Biomarkers in Cerebrospinal Fluid by FastCAT

Absolute (molar) quantification of proteins in cerebrospinal fluid (CSF) provides reference values and ranges of their physiological variation for perspective biomarkers across a broad spectrum of neurological disorders. FastCAT (for Fast-track QconCAT) method employs targeted mass spectrometry and multiple recombinant stable-isotope labeled chimeric proteins (CPs) as internal calibrants for the accurate and consistent determination of molar concentrations of dozens of CSF proteins. No purification or external quantification of CPs is required. We demonstrate that FastCAT, powered by parallel reaction monitoring (PRM) detection of multiple quantotypic peptides per target proteins, can quantify the molar concentration of neurological biomarkers from neat CSF over a dynamic range of more than 1000-fold, with high precision (coefficient of variation <20%) and low detection limits (<1 nmol/L) in a single LC-MS/MS analysis.