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

Abstract

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.

Trial registration: ClinicalTrials.gov NCT00392795.

Keywords: Ascertain Dementia 8; Clinical Dementia Rating Scale; Cognitive disorders; Cognitive screening test; Critical illness; Delirium; Dementia; Diagnosis; Sensitivity; Specificity.

Fig. 1.

Screening protocol for pre-existing cognitive impairment by surrogate assessment. ^a The Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) is a 16-item, informant-based screening tool [31]. IQCODE scores from 3.3 to 3.6 have been shown to be valid for the diagnosis of dementia in a variety of non-ICU settings [4]. ^b The Clinical Dementia Rating Scale (CDR) is a detailed surrogate-based questionnaire designed to detect and stage dementia and commonly used as a gold standard. Because the main aim of the BRAIN-ICU study was to identify potentially modifiable risk factors for long-term cognitive impairment after the ICU, patients with severe dementia (CDR score = 3) were excluded.

Fig. 2.

Study enrollment. Seventy-five patients had the Eight-Item Informant Interview to Differentiate Aging and Dementia (AD8; index test) and the Clinical Dementia Rating Scale (CDR; reference standard) completed and were included in this study.

Fig. 3.

Receiver operating characteristic curves for the Eight-Item Interview to Differentiate Aging and Dementia (AD8) as a screening tool for diagnosing dementia. Receiver operating characteristic curves are shown using the standard cutoff of ≥2 for the AD8. a Diagnostic performance of the AD8 for diagnosing very mild dementia (Clinical Dementia Rating Scale score ≥0.5). b Diagnostic performance of the AD8 for diagnosing mild dementia (Clinical Dementia Rating Scale score ≥1.0).