How accurate is the AD-8 informant questionnaire for diagnosing dementia in all healthcare settings?

Why is recognising dementia important?

Many people are living with dementia but have never had the condition diagnosed. Not recognising dementia when it is present (a false negative result) may deny people access to social support, medications, and financial assistance. It also prevents the individual and their family from planning for the future. However, incorrectly diagnosing dementia when it is not present (a false positive result) can cause distress or fear and lead to additional investigations which can waste resources.

What is the aim of the review?

The aim of this Cochrane Review was to find out how accurate the AD-8 informant questionnaire is for detecting dementia in all healthcare settings. The researchers included 10 studies to answer this question, nine of which reported numerical information that could be used.

What was studied in the review?

The AD-8 questionnaire includes eight ‘yes or no’ questions, to be answered by someone who knows the person under investigation; for example, a relative, carer or close friend (sometimes described as an informant). The questions ask about whether the informant has noticed a change in the individual’s memory and thinking abilities over the past years. A point is given for every item where they think the person’s abilities have changed. Higher scores occur when more changes are noted by the informant. The AD-8 would not usually be used to make a final diagnosis of dementia, but it may help identify those who require further assessment.

What are the main results of the review?

The review included data from nine relevant studies, with a total of 4045 participants.

Seven of the studies used a score of two or more to indicate dementia. A score of two or more is the cut-off recommended for the AD-8. The results of these studies indicate that, in theory, if the AD-8 were to be used to diagnose dementia in a group of 1000 people across all healthcare settings, of whom 280 (28%) have dementia, an estimated 517 would have an AD-8 result indicating dementia is present and of these 259 (50%) will not have dementia. Of the 483 people with a result indicating that dementia is not present, 22 (5%) would be incorrectly classified as not having dementia

It is possible that the AD-8 may work differently in different settings, for example in hospital or General practice. In secondary care, the AD-8 produces more false positive results, but fewer false negative results, than when it is used in community settings. We could not directly compare the performance of the AD-8 in primary care as there was only one study from this setting.

How reliable are the results of the studies in this review?

In the included studies, the diagnosis of dementia was made by assessing all patients with a detailed clinical assessment. (In these studies, detailed clinical assessment was the gold standard we compared the AD-8 to.) This is likely to have been a reliable method for deciding whether patients really had dementia. However, there were some problems with how the studies were conducted. This may have resulted in the AD-8 appearing more accurate than it really is. The numbers described are an average across studies in the review. However, as estimates from individual studies varied we cannot be sure that the AD-8 will always produce these results.

Who do the results of this review apply to?

Studies included in the review were conducted in Brazil, China, Japan, Singapore, Taiwan, the UK and USA. Studies included those attending primary and secondary care services, and populations of older adults living in the community. Five studies used the English-language version of the AD-8. The percentage of people with a final diagnosis of dementia was between 12% and 90% (an average of 38%).

What are the implications of this review?

The studies included in this review suggest the AD-8 can identify adults who may have a diagnosis of dementia, who would benefit from specialist assessment and diagnosis. If the AD-8 was used alone to diagnose dementia, the chance of wrongly diagnosing someone with dementia when they do not actually have it is high (50% of those whose AD-8 score suggests they have dementia). This makes the AD-8 an unsuitable single diagnostic test as it would potentially create anxiety and distress. The chance of missing a diagnosis of dementia is much lower (5% of those whose AD-8 score suggests they do not have dementia when they actually have it). This group will miss out on opportunities to plan their future care and would not be eligible to be assessed for treatment with medicines. These findings should be considered when deciding whether or not to use the AD-8 to test for dementia.

How up-to-date is this review?

The review authors searched for and used studies published up to June 2018.

Authors' conclusions: 

The high sensitivity of the AD-8 suggests it can be used to identify adults who may benefit from further specialist assessment and diagnosis, but is not a diagnostic test in itself. This pattern of high sensitivity and lower specificity is often suited to a screening test. Test accuracy varies by setting, however data in primary care and acute hospital settings are limited. This review identified significant heterogeneity and risk of bias, which may affect the validity of its summary findings.

Read the full abstract...
Background: 

Dementia assessment often involves initial screening, using a brief tool, followed by more detailed assessment where required. The AD-8 is a short questionnaire, completed by a suitable 'informant' who knows the person well. AD-8 is designed to assess change in functional performance secondary to cognitive change.

Objectives: 

To determine the diagnostic accuracy of the informant-based AD-8 questionnaire, in detection of all-cause (undifferentiated) dementia in adults. Where data were available, we described the following: the diagnostic accuracy of the AD-8 at various predefined threshold scores; the diagnostic accuracy of the AD-8 for each healthcare setting and the effects of heterogeneity on the reported diagnostic accuracy of the AD-8.

Search strategy: 

We searched the following sources on 27 May 2014, with an update to 7 June 2018: ALOIS (Cochrane Dementia and Cognitive Improvement Group), MEDLINE (Ovid SP), Embase (Ovid SP), PsycINFO (Ovid SP), BIOSIS Previews (Thomson Reuters Web of Science), Web of Science Core Collection (includes Conference Proceedings Citation Index) (Thomson Reuters Web of Science), CINAHL (EBSCOhost) and LILACS (BIREME). We checked reference lists of relevant studies and reviews, used searches of known relevant studies in PubMed to track related articles, and contacted research groups conducting work on the AD-8 to try to find additional studies. We developed a sensitive search strategy and used standardised database subject headings as appropriate. Foreign language publications were translated.

Selection criteria: 

We selected those studies which included the AD-8 to assess for the presence of dementia and where dementia diagnosis was confirmed with clinical assessment. We only included those studies where the AD-8 was used as an informant assessment. We made no exclusions in relation to healthcare setting, language of AD-8 or the AD-8 score used to define a 'test positive' case.

Data collection and analysis: 

We screened all titles generated by electronic database searches, and reviewed abstracts of potentially relevant studies. Two independent assessors checked full papers for eligibility and extracted data. We extracted data into two-by-two tables to allow calculation of accuracy metrics for individual studies. We then created summary estimates of sensitivity, specificity and likelihood ratios using the bivariate approach and plotting results in receiver operating characteristic (ROC) space. We determined quality assessment (risk of bias and applicability) using the QUADAS-2 tool.

Main results: 

From 36 papers describing AD-8 test accuracy, we included 10 papers. We utilised data from nine papers with 4045 individuals, 1107 of whom (27%) had a clinical diagnosis of dementia. Pooled analysis of seven studies, using an AD-8 informant cut-off score of two, indicated that sensitivity was 0.92 (95% confidence interval (CI) 0.86 to 0.96); specificity was 0.64 (95% CI 0.39 to 0.82); the positive likelihood ratio was 2.53 (95% CI 1.38 to 4.64); and the negative likelihood ratio was 0.12 (95% CI 0.07 to 0.21). Pooled analysis of five studies, using an AD-8 informant cut-off score of three, indicated that sensitivity was 0.91 (95% CI 0.80 to 0.96); specificity was 0.76 (95% CI 0.57 to 0.89); the positive likelihood ratio was 3.86 (95% CI 2.03 to 7.34); and the negative likelihood ratio was 0.12 (95% CI 0.06 to 0.24).

Four studies were conducted in community settings; four were in secondary care (one in the acute hospital); and one study was in primary care. The AD-8 has a higher relative sensitivity (1.11, 95% CI 1.02 to 1.21), but lower relative specificity (0.51, 95% CI 0.23 to 1.09) in secondary care compared to community care settings.

There was heterogeneity across the included studies. Dementia prevalence rate varied from 12% to 90% of included participants. The tool was also used in various different languages. Among all the included studies there was evidence of risk of bias. Issues included the selection of participants, conduct of index test, and flow of assessment procedures.

Share/Save