Why Is Amyloid-β PET Requested After Performing CSF Biomarkers?

J Alzheimers Dis. 2020;73(2):559-569. doi: 10.3233/JAD-190836.


Background: Amyloid-β positron emission tomography (PET) and cerebrospinal fluid (CSF) Aβ42 are considered interchangeable for clinical diagnosis of Alzheimer's disease.

Objective: To explore the clinical reasoning for requesting additional amyloid-β PET after performing CSF biomarkers.

Methods: We retrospectively identified 72 memory clinic patients who underwent amyloid-β PET after CSF biomarkers analysis for clinical diagnostic evaluation between 2011 and 2019. We performed patient chart reviews to identify factors which led to additional amyloid-β PET. Additionally, we assessed accordance with appropriate-use-criteria (AUC) for amyloid-β PET.

Results: Mean patient age was 62.0 (SD = 8.1) and mean Mini-Mental State Exam score was 23.6 (SD = 3.8). CSF analysis conflicting with the clinical diagnosis was the most frequent reason for requesting an amyloid-β PET scan (n = 53, 74%), followed by incongruent MRI (n = 16, 22%), unusual clinical presentation (n = 11, 15%) and young age (n = 8, 11%). An amyloid-β PET scan was rarely (n = 5, 7%) requested in patients with a CSF Aβ+/tau+ status. Fifteen (47%) patients with a post-PET diagnosis of AD had a predominantly non-amnestic presentation. In n = 11 (15%) cases, the reason that the clinician requested amyloid-β was not covered by AUC. This happened most often (n = 7) when previous CSF analysis did not support current clinical diagnosis, which led to requesting amyloid-β PET.

Conclusion: In this single-center study, the main reason for requesting an amyloid-β PET scan after performing CSF biomarkers was the occurrence of a mismatch between the primary clinical diagnosis and CSF Aβ/tau results.

Keywords: Alzheimer’s disease; amyloid; cerebrospinal fluid; positron emission tomography; tau proteins.

MeSH terms

  • Aged
  • Alzheimer Disease / cerebrospinal fluid
  • Alzheimer Disease / diagnostic imaging
  • Alzheimer Disease / psychology
  • Amyloid beta-Peptides / cerebrospinal fluid*
  • Biomarkers / cerebrospinal fluid*
  • Female
  • Humans
  • Magnetic Resonance Imaging
  • Male
  • Mental Status and Dementia Tests
  • Middle Aged
  • Neuropsychological Tests
  • Peptide Fragments / cerebrospinal fluid
  • Physicians
  • Positron-Emission Tomography*
  • Retrospective Studies
  • tau Proteins / cerebrospinal fluid


  • Amyloid beta-Peptides
  • Biomarkers
  • Peptide Fragments
  • amyloid beta-protein (1-42)
  • tau Proteins