It is necessary to continue to explore the psychometric characteristics of key cognitive screening tests such as the Montreal Cognitive Assessment (MoCA) to diagnose cognitive decline as early as possible and to attend to the growing need of clinical trials involving mild cognitive impairment (MCI) participants. The main aim of this study was to assess which MoCA subtests could best discriminate between healthy controls (HC), participants with MCI, and Alzheimer's disease (AD).

Cross-sectional analysis of 136 elderly with more than four years of education. All participants were submitted to detailed clinical, laboratory, and neuroimaging evaluation. The MoCA, Mini-Mental State Examination (MMSE), the Cambridge Cognitive Examination (CAMCOG), Geriatric Depression Scale (GDS), and Functional Activities Questionnaire (FAQ) were applied to all participants. The MoCA test was not used in the diagnostic procedure.

Median MoCA total scores were 27, 23 and 18 for HC, MCI, and AD, respectively (p < 0.001). Word repetition, inverse digits, serial 7, phrases, verbal fluency, abstraction, and word recall discriminated between MCI and HC participants (p < 0.001). The clock drawing, the rhino naming, delayed recall of five words and orientation discriminated between patients with MCI and AD (p < 0.001). A reduced version of the MoCA with only these items did not improve accuracy between MCI and HC (p = 0.076) or MCI and AD (p = 0.119).

Not all MoCA subtests might be fundamental to clinical diagnosis of MCI. The reduced versions of MoCA did not add diagnostic accuracy.