Tau and Aβ42 in Cerebrospinal Fluid from Healthy Adults 21–93 Years of Age: Establishment of Reference Values

BACKGROUND: Tau protein and the 42-amino acid form of beta-amyloid (Abeta42) measured in cerebrospinal fluid (CSF) have been proposed as potential biochemical diagnostic markers for Alzheimer disease. For the introduction of these assays in clinical practice, adequate reference values are of importance. METHODS: CSF samples were obtained from 231 neurologically and psychiatrically healthy individuals, 21-93 years of age, all with a MiniMental State examination score of 28 or above. Standardized ELISAs were used to measure tau and Abeta42 in CSF. Following IFCC recommendations, we used a rank-based method; the 0.90 and 0.10 fractiles were estimated to establish reference values for CSF-tau and CSF-Abeta42, respectively. Putative confounding factors, such as the influence of the passage of proteins from peripheral blood to CSF, influence of dysfunction of the blood-brain barrier, and freezing and thawing of CSF, were investigated. RESULTS: A correlation with age was found for CSF-tau (r = 0.60; P 500 ng/L. No correlation was found between blood-brain barrier function and CSF-tau or CSF-Abeta42. CONCLUSIONS: These reference values can be applied when using CSF-tau and CSF-Abeta42 in clinical practice.