CSF tau protein andβ‐amyloid (1–42) in Alzheimer's disease diagnosis: discrimination from normal ageing and other dementias in the Greek population

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Abstract
Cerebrospinal fluid (CSF) levels of tau protein and amyloidβ(1–42) peptide (Aβ42) have been suggested as possible diagnostic markers of Alzheimer's disease (AD). In order to evaluate their diagnostic potential in clinical practice, we measured tau and Aβ42 levels in the CSF of 49 AD patients, 15 patients with non‐AD neurodegenerative dementias (NAND), six patients with vascular dementia (VD) and 49 elderly controls. All the subjects were of Greek origin. A marked increase in tau, a decrease in Aβ42 and a marked increase in the tau/Aβ42 ratio was noted in AD. Aβ42 alone had a specificity of 80% and a sensitivity of 82% in differentiating AD from normal ageing, whilst the corresponding values for differentiating AD from NAND or VD were 80 and 71, or 67 and 82%, respectively. Tau was better in differentiating AD, from normal ageing (specificity 96%, sensitivity 88%), NAND (specificity 93%, sensitivity 71%) and VD (specificity 83%, sensitivity 94%). The tau/Aβ42 ratio achieved values comparable or even better than tau for differentiating AD from normal ageing (specificity 86%, sensitivity 96%) and VD (specificity 83%, sensitivity 90%) and definitely better than any of the candidate markers alone, for differentiating AD from NAND (specificity 100%, sensitivity 71%). Thus, the combined use of CSF tau and Aβ42 in the form of the tau/Aβ42 ratio is a simple, safe and useful adjuvant to clinical criteria for dementia diagnosis.