further specialist investigations if Alzheimer's disease suspected

Last edited 05/2022

If the diagnosis is uncertain and Alzheimer's disease is suspected, consider either:

  • FDG-PET (fluorodeoxyglucose-positron emission tomography-CT), or perfusion SPECT (single-photon emission CT) if FDG-PET is unavailable or
  • examining cerebrospinal fluid for:
    • either total tau or total tau and phosphorylated-tau 181 and
    • either amyloid beta 1-42 or amyloid beta 1-42 and amyloid beta 1-40
  • If a diagnosis cannot be made after one of these tests, consider using the other one.


  • the older a person is, the more likely they are to get a false positive with CSF fluid exam
  • do not rule out Alzheimer's disease based solely on the results of CT or MRI scans.
  • do not use apolipoprotein E genotyping or electroencephalography to diagnose AD
  • be aware that young-onset Alzheimer's disease has a genetic cause in some people.