Is the Alzheimer's Disease Assessment Scale-Cognitive Subscale useful in screening for mild cognitive impairment and Alzheimer's disease? A systematic review.

BACKGROUND Mild cognitive impairment (MCI) and Alzheimer's disease (AD) are screened to distinguish whether cognitive decline in older adults is attributed to pathological causes rather than normal aging. OBJECTIVE The purpose of this review was to analyze the diagnostic performance of the Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog) in screening for MCI and AD. METHODS Electronic searches were performed on MEDLINE, EMBASE, CINAHL, and PsycArticles databases using the following keywords: dementia and ADAS-Cog. The Quality Assessment of Diagnostic Accuracy Studies-2 was used to checked the risk of bias in the diagnostic studies. RESULTS We reviewed 14 studies, including 3,875 patients who met the selection criteria. In 2,624 MCI patients from nine studies, the pooled sensitivity of ADAS-Cog was 0.80 (95% confidence interval [CI], 0.68-0.88), the pooled specificity was 0.84 (95% CI, 0.75-0.90), and the area under the curve of summary receiver-operating characteristic curves (SROC AUC) was 0.89 (SE = 0.03). In 2,517 AD patients from 10 studies, the pooled sensitivity and pooled specificity were 0.91 (95% CI, 0.86-0.95) and 0.93 (95% CI, 0.88-0.95) respectively, and the sROC AUC was 0.97 (SE = 0.01). Although sub-analyzed according to age and years of education, there was no significant difference in the predictive validity of the ADAS-Cog. CONCLUSION The ADAS-Cog has high predictive validity as a screening tool in both MCI and AD, but has better diagnostic performance in patients with AD. When early screening for AD is desired, ADAS-Cog is a first-stage screener that can be initially employed.