title: Olfactory identification testing as a predictor of the development of Alzheimer's dementia: a systematic review.
abstract: OBJECTIVE
  To evaluate the utility of olfactory identification tests as prognostic instruments for Alzheimer's dementia (AD).
  
  
  METHODS
  Systematic review.
  
  
  METHODS
  In accordance with PRISMA guidelines, PubMed and Ovid MEDLINE, EMBASE, ISI Web of Science, PsycINFO, the Cochrane Database of Systematic Reviews, and the Cochrane Central Register of Controlled Trials were searched to determine the quality and quantity of longitudinal and cross-sectional research on this topic.
  
  
  RESULTS
  Two prospective longitudinal cohort studies and 30 cross-sectional studies met inclusion criteria. The prospective longitudinal studies evaluated subjects with or without mild cognitive impairment (MCI) while also using olfactory identification testing as part of a neurocognitive evaluation. The first study reported an increased risk of later onset of AD in subjects with baseline hyposmia, whereas the second study suggested a possible relationship between decreased olfaction in participants with MCI and conversion to AD but was inconclusive due to low follow-up rates. Wide variability in the type of olfactory identification test used and the reporting of results precluded meta-analysis. The cross-sectional studies demonstrated a positive association between poorer performance on olfactory identification testing and AD.
  
  
  CONCLUSIONS
  Although there is evidence suggesting an association between decreased olfaction and AD, rigorously designed longitudinal cohort studies are necessary to clarify the value of olfactory identification testing in predicting the onset of AD.
authors.affiliation: Robert Wood Johnson Foundation Clinical Scholars, University of Michigan, Ann Arbor, Michigan, USA. gordonsu@med.umich.edu
authors.forename: Gordon H
authors.initials: GH
authors.lastname: Sun
authors.forename: Cyrus A
authors.initials: CA
authors.lastname: Raji
authors.forename: Mark P
authors.initials: MP
authors.lastname: Maceachern
authors.forename: James F
authors.initials: JF
authors.lastname: Burke
mesh_terms: D000544:Alzheimer Disease; D006801:Humans; D011237:Predictive Value of Tests; D011379:Prognosis; D012903:Smell