EvidenceAlerts

MacLullich AM, Shenkin SD, Goodacre S, et al. The 4 'A's test for detecting delirium in acute medical patients: a diagnostic accuracy study. Health Technol Assess. 2019 Aug;23(40):1-194. doi: 10.3310/hta23400. (Original study)
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.

Delirium is the sudden onset of confusion that can happen when someone is unwell. It is common in older people who go into hospital, and it is upsetting for both the patients and their families. Delirium is important to diagnose, because people with delirium do less well than those without, and it is often treatable. The ideal way to diagnose delirium is with a full assessment by a specialist, but this is expensive and time-consuming. We therefore developed a short test called the 4 ‘A’s Test (4AT). The four ‘A’s stand for Arousal, Attention, Abbreviated Mental Test – 4, and Acute change. First, we interviewed hospital staff about delirium and the 4AT. We found that the 4AT was already widely used and that people found it easy to use. We then tested how the 4AT performed in practice. A total of 785 recently admitted patients aged = 70 years participated, of whom around one in eight had delirium. A researcher carried out the full standard delirium assessment on each patient and then a different researcher carried out the 4AT. A normal 4AT score reliably ruled out delirium. An abnormal score was also reasonably effective in detecting delirium, but staff still needed to follow up such patients with a full assessment. People with higher 4AT scores stayed in hospital longer and were more likely to die, and their treatment was more expensive. We conclude that the 4AT is a useful test to rule out delirium or to see if more detailed testing is required. It could help treat patients correctly and quickly. This would save money and improve outcomes.


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Ratings
Discipline Area Score
Hospital Doctor/Hospitalists 7 / 7
Internal Medicine 7 / 7
Geriatrics 6 / 7
Emergency Medicine 5 / 7
Comments from MORE raters

Emergency Medicine rater

In the ED, there is a need for a quick screening tool for delirium, given the clinical morbidity and resource use implications. This very extensive health technology assessment looked at implementation barriers as well as clinical performance of the 4AT and CAM, compared to a more extensive reference standard. This very comprehensive study is a well designed RCT. Generalization to the ED is limited as <10% of patients were screened in the ED. Additionally, there was high attrition rates, mostly because of issues around consent. The number of patients enrolled was less than the number required for the stated power. Finally, of patients who actually had delirium, the performance of either tool was sub-optimal. However, the results do demonstrate that both the CAM and 4AT preform well at ruling out delirium. For me, using either tool can be helpful as a quick rule-out; however, positive CAM or 4AT indicates the need for further assessment.

Emergency Medicine rater

Delirium is frequently overlooked by emergency physicians (EPs). This is a 193 page assessment of the 4 "A"s test that screens for delirium in acute medical patients. The test was found to be a useful rule out tool, i.e. a low score rules out delirium. The assessment of the tool is exhaustive and exhausting to look through. Most EPs will not be interested in reading it. The 4 As test itself is found on p.54 for those who want to save time finding it! Routine use of it would be helpful, but probably no more than raising the awareness of EPs to consider the possibility of delirium in the patient in front of them.

Geriatrics rater

In North America, CAM is already in wide use so most practitioners will not change their assessment tool unless the 4AT is shown to be superior.
Comments from EvidenceAlerts subscribers

Dr. Kenneth Lee (8/26/2019 9:21 PM)

I can’t seem to understand why the 4-AT is a good tool for ruling OUT delirium given that its specificity is much higher in proportion to its sensitivity. Can anyone elaborate?