A method, a labeling reagent, sets of labeling reagents, and labeling techniques are provided for the analysis of ketosterol biomarkers such as bile acid precursors from human plasma, serum or whole blood. This method is used for new born screening for Cerebrotendinous Xanthomatosis (CTX). Methods for labeling, analyzing, and quantifying ketosterol biomarkers are also disclosed as are methods that also use mass spectrometry.