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The 4 ‘A’s test for detecting delirium in acute medical patients: a diagnostic accuracy study

MacLullich, Alasdair MJ; Shenkin, Susan D; Goodacre, Steve; Godfrey, Mary; Hanley, Janet; Stíobhairt, Antaine; Lavender, Elizabeth; Boyd, Julia; Stephen, Jacqueline; Weir, Christopher; MacRaild, Allan; Steven, Jill; Black, Polly; Diernberger, Katharina; Hall, Peter; Tieges, Zoë; Fox, Christopher; Anand, Atul; Young, John; Siddiqi, Najma; Gray, Alasdair

Authors

Alasdair MJ MacLullich

Susan D Shenkin

Steve Goodacre

Mary Godfrey

Antaine Stíobhairt

Elizabeth Lavender

Julia Boyd

Jacqueline Stephen

Christopher Weir

Allan MacRaild

Jill Steven

Polly Black

Katharina Diernberger

Peter Hall

Zoë Tieges

Christopher Fox

Atul Anand

John Young

Najma Siddiqi

Alasdair Gray



Abstract

Background: Delirium is a common and serious neuropsychiatric syndrome, usually triggered by illness or drugs. It remains underdetected. One reason for this is a lack of brief, pragmatic assessment tools. The 4 ‘A’s test (Arousal, Attention, Abbreviated Mental Test – 4, Acute change) (4AT) is a screening tool designed for routine use. This project evaluated its usability, diagnostic accuracy and cost.

Methods: Phase 1 – the usability of the 4AT in routine practice was measured with two surveys and two qualitative studies of health-care professionals, and a review of current clinical use of the 4AT as well as its presence in guidelines and reports. Phase 2 – the 4AT’s diagnostic accuracy was assessed in newly admitted acute medical patients aged ≥ 70 years. Its performance was compared with that of the Confusion Assessment Method (CAM; a longer screening tool). The performance of individual 4AT test items was related to cognitive status, length of stay, new institutionalisation, mortality at 12 weeks and outcomes. The method used was a prospective, double-blind diagnostic test accuracy study in emergency departments or in acute general medical wards in three UK sites. Each patient underwent a reference standard delirium assessment and was also randomised to receive an assessment with either the 4AT (n = 421) or the CAM (n = 420). A health economics analysis was also conducted.

Results: Phase 1 found evidence that delirium awareness is increasing, but also that there is a need for education on delirium in general and on the 4AT in particular. Most users reported that the 4AT was useful, and it was in widespread use both in the UK and beyond. No changes to the 4AT were considered necessary. Phase 2 involved 785 individuals who had data for analysis; their mean age was 81.4 (standard deviation 6.4) years, 45% were male, 99% were white and 9% had a known dementia diagnosis. The 4AT (n = 392) had an area under the receiver operating characteristic curve of 0.90. A positive 4AT score (> 3) had a specificity of 95% [95% confidence interval (CI) 92% to 97%] and a sensitivity of 76% (95% CI 61% to 87%) for reference standard delirium. The CAM (n = 382) had a specificity of 100% (95% CI 98% to 100%) and a sensitivity of 40% (95% CI 26% to 57%) in the subset of participants whom it was possible to assess using this. Patients with positive 4AT scores had longer lengths of stay (median 5 days, interquartile range 2.0–14.0 days) than did those with negative 4AT scores (median 2 days, interquartile range 1.0–6.0 days), and they had a higher 12-week mortality rate (16.1% and 9.2%, respectively). The estimated 12-week costs of an initial inpatient stay for patients with delirium were more than double the costs of an inpatient stay for patients without delirium (e.g. in Scotland, £7559, 95% CI £7362 to £7755, vs. £4215, 95% CI £4175 to £4254). The estimated cost of false-positive cases was £4653, of false-negative cases was £8956, and of a missed diagnosis was £2067.

Limitations: Patients were aged ⋝ 70 years and were assessed soon after they were admitted, limiting generalisability. The treatment of patients in accordance with reference standard diagnosis limited the ability to assess comparative cost-effectiveness.

Conclusions: These findings support the use of the 4AT as a rapid delirium assessment instrument. The 4AT has acceptable diagnostic accuracy for acute older patients aged > 70 years.

Future work: Further research should address the real-world implementation of delirium assessment. The 4AT should be tested in other populations.

Trial registration: Current Controlled Trials ISRCTN53388093.

Funding: This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 23, No. 40. See the NIHR Journals Library website for further project information. The funder specified that any new delirium assessment tool should be compared against the CAM, but had no other role in the study design or conduct of the study.

Citation

MacLullich, A. M., Shenkin, S. D., Goodacre, S., Godfrey, M., Hanley, J., Stíobhairt, A., Lavender, E., Boyd, J., Stephen, J., Weir, C., MacRaild, A., Steven, J., Black, P., Diernberger, K., Hall, P., Tieges, Z., Fox, C., Anand, A., Young, J., Siddiqi, N., & Gray, A. (2019). The 4 ‘A’s test for detecting delirium in acute medical patients: a diagnostic accuracy study. Health Technology Assessment, 23(40), 1-194. https://doi.org/10.3310/hta23400

Journal Article Type Article
Acceptance Date Oct 2, 2018
Publication Date 2019-08
Deposit Date Oct 23, 2018
Publicly Available Date Aug 9, 2019
Journal Health Technology Assessment
Print ISSN 1366-5278
Publisher NIHR Journals Library
Peer Reviewed Peer Reviewed
Volume 23
Issue 40
Pages 1-194
DOI https://doi.org/10.3310/hta23400
Keywords Delirium, dementia, acute hospitals, 4AT, diagnostic accuracy, CAM
Public URL http://researchrepository.napier.ac.uk/Output/1320630
Publisher URL https://www.journalslibrary.nihr.ac.uk/hta/#/
Contract Date Oct 23, 2018

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Copyright Statement
Permission to reproduce material from a published report is covered by the UK government’s non-commercial licence for public sector information. http://www.nationalarchives.gov.uk/doc/non-commercial-government-licence/version/2/

Contains information licensed under the Non-Commercial Government Licence v2.0. Use of this information is for non-commercial purposes only.








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