Amyloid PETs are commonly negative in suspected Alzheimer's disease with an increase in CSF phosphorylated-tau protein concentration but an Aβ42 concentration in the very high range: a prospective study.

In mild neurocognitive disorders patients with suspected AD and showing an increase in CSF P-tau protein level, amyloid PETs are commonly negative, when Aß42 concentration is in the very high range. In such case, AD diagnosis based on biomarkers can be ruled out with reasonable certainty, without the need for additional CSF second-line assays or results from amyloid PET.