NEFL and neurodegenerative disease: With regard to correlations of markers across biofluids, several past studies have compared disease biomarkers between CSF and blood, and these studies have shown that levels of two widely studies neurodegenerative disease biomarker, neurofilament light (NfL) and glial fibrillary acidic protein (GFAP), among others, are significantly positively correlated between CSF and blood in patients with neurodegenerative diseases [14, 15].