Do the ABCS 135 short cognitive screen and its subtests discriminate between normal cognition, mild cognitive impairment and dementia?

BACKGROUND: Cognitive screening instruments are either too long for routine clinical use or not sensitive to distinguish mild cognitive impairment (MCI) from normal cognition (NC) or dementia.

OBJECTIVE: To evaluate the sensitivity and specificity of the AB Cognitive Screen (ABCS) and its subtests with a view to improving its ability to differentiate between dementia, MCI and NC. The influence of age and education on sensitivity and specificity is also examined.

DESIGN: Cross-sectional study.

METHODS: Participants with dementia and MCI were recruited from those presenting to four specialty geriatric clinics in southern Ontario. Participants with NC were recruited from the family and friends of patients. A comprehensive geriatric assessment was done including ABCS, SMMSE and 15 point Geriatric Depression Scale. Analysis of variance and receiver operating characteristic (ROC) curves compared test scores. SMMSE scores were also analysed for comparison purposes.

RESULTS: Three hundred and two participants had dementia, 166 had MCI and 174 had NC. ABCS total scores were significantly different between NC and MCI (mean difference 7.1, 1.8-12.5 CI, p = 0.000) while SMMSE scores were not (mean difference 0.5, -0.7-1.7, p < 0.628). Of individual ABCS subtests, verbal fluency and delayed recall were most sensitive to differences between NC and MCI. ROC curve analysis, which presents sensitivity and specificity, showed verbal fluency was better than delayed recall in distinguishing between NC and MCI, among participants 75 years of age or older.

CONCLUSION: The AB Cognitive Screen (ABCS) can be administered in 3-5 min. The SMMSE and ABCS total and subtests significantly distinguished between dementia and MCI or NC. Verbal fluency and delayed recall were best at distinguishing between MCI and NC. The analysis illustrates how each subtest contributes to the sensitivity of the ABCS and suggests ways that sensitivity might be improved.