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

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  • Steve Goodacre
  • Mary Godfrey
  • Janet Hanley
  • Antaine Stiobhairt
  • Elizabeth Lavender
  • Allan Macraild
  • Jill Steven
  • Polly Black
  • C. Fox
  • A. Anand
  • J. Young
  • N. Siddiqi
  • A. Gray

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  • AAM - The 4 As Test (4AT) delirium assessment...

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    Rights statement: Queen’s Printer and Controller of HMSO 2019. This work was produced by MacLullich et al. under the terms of a commissioning contract issued by the Secretary of State for Health and Social Care. This issue may be freely reproduced for the purposes of private research and study and extracts (or indeed, the full report) may be included in professional journals provided that suitable acknowledgement is made and the reproduction is not associated with any form of advertising. Applications for commercial reproduction should be addressed to: NIHR Journals Library, National Institute for Health Research, Evaluation, Trials and Studies Coordinating Centre, Alpha House, University of Southampton Science Park, Southampton SO16 7NS, UK.

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Original languageEnglish
Pages (from-to)1-+
Number of pages195
JournalHealth Technology Assessment
Volume23
Issue number40
DOIs
Publication statusPublished - Aug 2019

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 pound, 95% CI 7362 pound to 7755 pound, vs. 4215 pound, 95% CI 4175 pound to 4254) pound. The estimated cost of false-positive cases was 4653 pound, of false-negative cases was 8956 pound, and of a missed diagnosis was 2067 pound.

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.

    Research areas

  • INTENSIVE-CARE-UNIT, CONFUSION ASSESSMENT METHOD, ABBREVIATED MENTAL TEST, EMERGENCY-DEPARTMENT, COGNITIVE IMPAIRMENT, ELDERLY-PATIENTS, OLDER-PEOPLE, PALLIATIVE CARE, HIP FRACTURE, RISK-FACTORS

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