A Brief Informant Screening Instrument for Dementia in the ICU: The Diagnostic Accuracy of the AD8 in Critically Ill Adults Suspected of Having Pre-Existing Dementia

Background/Aim: The diagnostic accuracy of brief informant screening instruments to detect dementia in critically ill adults is unknown. We sought to determine the diagnostic accuracy of the 2- to 3-min Ascertain Dementia 8 (AD8) completed by surrogates in detecting dementia among critically ill adults suspected of having pre-existing dementia by comparing it to the Clinical Dementia Rating Scale (CDR). Methods: This substudy of BRAIN-ICU included a subgroup of 75 critically ill medical/surgical patients determined to be at medium risk of having pre-existing dementia (Informant Questionnaire on Cognitive Decline in the Elderly [IQCODE] score ≥3.3). We calculated the sensitivity, specificity, positive and negative predictive values (PPV and NPV), and AUC for the standard AD8 cutoff of ≥2 versus the reference standard CDR score of ≥1 for mild dementia. Results: By the CDR, 38 patients had very mild or no dementia and 37 had mild dementia or greater. For diagnosing mild dementia, the AD8 had a sensitivity of 97% (95% CI 86–100), a specificity of 16% (6–31), a PPV of 53% (40–65), an NPV of 86% (42–100), and an AUC of 0.738 (0.626–0.850). Conclusions: Among critically ill patients judged at risk for pre-existing dementia, the 2- to 3-min AD8 is highly sensitive and has a high NPV. These data indicate that the brief tool can serve to rule out dementia in a specific patient population.