About delirium and its assessment
Delirium is one of the most common and most serious acute conditions in hospital — and one of the most frequently missed. Understanding what it is, and how assessment tools differ, is the first step to detecting it reliably.
Urgent medical assessment
Sudden new confusion, drowsiness or altered behaviour needs urgent medical assessment. This website cannot diagnose delirium or advise on an individual patient.
What delirium is
Delirium is an acute, usually fluctuating disturbance of attention and awareness, accompanied by additional changes in cognition, that develops over hours to days and is caused by an underlying medical problem — infection, medication, surgery, metabolic disturbance, and many others. Its hallmark is inattention, and its course typically fluctuates through the day.
Motor activity may be hyperactive (agitated, restless), hypoactive (drowsy, withdrawn, quiet) or mixed; some patients do not fit a motor subtype. Hypoactive presentations are common and particularly easy to miss.
Why detection matters
Frequency varies markedly by population and method. NICE estimates a prevalence of about 20–30% on hospital medical wards. A systematic review estimated 15.2% among older adults assessed in emergency departments, while a meta-analysis identified delirium in 31.8% of adults across 42 intensive-care studies. These are setting-level estimates, not predictions for an individual patient. Delirium is associated with longer stays, mortality, loss of independence and later cognitive decline. Recognition allows urgent assessment and treatment of underlying causes, but screening alone has not been shown to prevent all associated harm. NICE context; Chen et al. 2022; Salluh et al. 2015.
The recognition gap
Hypoactive and mixed presentations can be particularly difficult to recognise. Validated assessment tools support more consistent detection, and structured assessment is recommended in clinical guidance. NICE context.
How the tools differ
The instruments in this directory are not interchangeable, but neither do they form a simple screening-to-diagnosis ladder. They differ across several dimensions:
Assess for current delirium using an appropriate structured tool and clinical workflow.
Quantify severity and track change over time (e.g. MDAS, DRS-R-98, CAM-S).
Describe repeated observation across a shift or episode of care (e.g. NuDESC, DOSS, RADAR).
Draw on family or carer observation when recent change or baseline is important (e.g. SQiD, FAM-CAM).
Record contexts such as intensive care or paediatrics separately from clinical role (e.g. CAM-ICU, CAPD).
Estimate who may develop delirium later, rather than whether delirium is present now.
The practical categories provide simple routes based on when a tool is used, its setting or population, its information source and what it measures.
What makes a good bedside tool
- Brief and feasible in the time clinicians actually have.
- Minimal training — or clearly specified training — so results are consistent between staff.
- Assesses attention, acute change or fluctuation, and relevant changes in arousal without assuming that arousal is always abnormal.
- Validated in your setting and population against a proper reference standard.
- Usable in drowsy or uncooperative patients, not only in those who can fully engage.
Sources: NICE CG103 context (medical-ward estimate and recognition difficulty); Chen F, et al. Prevalence of delirium in older adults in the ED, 2022 (pooled 15.2%; PMID 35841845); Salluh JIF, et al. Outcome of delirium in critically ill patients, 2015 (5,280/16,595 adults across 42 ICU studies; PMID 26041151). Estimates vary with population and assessment method. This page is medical information, not individual clinical advice.