4AT Score Calculator

Hyperactive delirium presents with psychomotor agitation, restlessness, hallucinations, and emotional lability. Although dramatic and easier to recognise, it accounts for only about 25% of cases. Patients may pull at lines, attempt to leave the bed, or become combative.

Hypoactive delirium is characterised by lethargy, reduced responsiveness, slowed psychomotor activity, and social withdrawal. It is the most common subtype (up to 50% of cases) and is frequently misattributed to depression, fatigue, or sedation. Hypoactive delirium carries a worse prognosis and is the subtype most commonly missed by clinical teams.

Mixed delirium involves fluctuation between hyperactive and hypoactive features, often within the same day. This subtype accounts for approximately 25% of cases and can be particularly challenging to recognise because the periods of apparent calm may be mistaken for improvement.

The mnemonic DELIRIUMS provides a systematic approach to identifying precipitating causes:

• D — Drugs (anticholinergics, benzodiazepines, opioids, steroids, polypharmacy)
• E — Electrolyte disturbances (hyponatraemia, hypercalcaemia, hypo/hyperglycaemia)
• L — Lack of drugs (alcohol or benzodiazepine withdrawal)
• I — Infection (urinary tract, pneumonia, skin/soft tissue, intra-abdominal)
• R — Reduced sensory input (missing hearing aids, glasses; unfamiliar environment)
• I — Intracranial pathology (stroke, haemorrhage, seizure, meningitis)
• U — Urinary retention / faecal impaction (often overlooked)
• M — Myocardial / pulmonary (MI, PE, heart failure, hypoxia)
• S — Surgery / anaesthesia (post-operative delirium is extremely common)

Multiple precipitants frequently co-exist. A systematic review of all potential causes is essential, as treating only one may not resolve the delirium.

Delirium results from an interaction between predisposing vulnerability and precipitating insults. Patients with more predisposing factors require smaller precipitants to develop delirium — the “threshold model.” Key predisposing factors include:

• Advanced age (risk increases significantly after age 65)
• Pre-existing dementia — the single strongest risk factor; patients with dementia are 2–5 times more likely to develop delirium
• Frailty and functional dependence
• Sensory impairment (visual, hearing)
• Polypharmacy (≥5 medications)
• Malnutrition and dehydration
• History of prior delirium
• Depression
• Alcohol use disorder

The three Ds — delirium, dementia, and depression — frequently overlap and coexist, making differentiation challenging but critical:

Delirium has an acute onset (hours to days), a fluctuating course, disturbed attention as a core feature, and is often reversible with treatment of the underlying cause. Level of consciousness may be altered.

Dementia has an insidious onset (months to years), a progressive course, and relatively preserved attention in early stages. Level of consciousness is normal. Memory impairment tends to be the predominant early feature in Alzheimer’s type.

Depression may mimic hypoactive delirium with psychomotor slowing and withdrawal. However, onset is typically subacute (weeks), attention is generally preserved when tested, and mood symptoms predominate. Sleep-wake cycle disruption is common in both depression and delirium.

Crucially, delirium superimposed on dementia is extremely common — up to 65% of delirium occurs in patients with pre-existing cognitive impairment. The 4AT helps detect this by including items sensitive to both acute change and baseline cognitive impairment.

When the 4AT suggests possible delirium (score ≥4), a systematic evaluation should be initiated. The workup should be tailored to the clinical context but typically includes:

• Bloods: FBC, U&Es, LFTs, calcium, glucose, CRP, blood cultures (if febrile), thyroid function, B12/folate if not recently checked
• Urinalysis and culture — though asymptomatic bacteriuria is common in the elderly and should not be assumed to be the cause
• Chest radiograph — to exclude pneumonia or pulmonary oedema
• ECG — to screen for arrhythmia, myocardial ischaemia
• Medication review — comprehensive review of all current medications, recent changes, and over-the-counter agents
• Neuroimaging (CT head) — if focal neurological signs, history of falls/head injury, or if no clear precipitant is identified
• Lumbar puncture — if meningitis or encephalitis is suspected

Collateral history from family, carers, or nursing staff is essential to establish baseline cognitive function and the timeline of any change.

Before performing the 4AT, review the clinical record for any documented baseline cognitive impairment, prior episodes of delirium, current medications (especially recent additions or changes), and recent clinical events (surgery, infection, falls). Speak briefly with the nursing team or family if available to establish the patient’s usual cognitive and functional baseline — this information is essential for scoring Item 4 accurately.

Observe the patient before speaking. Are they awake, drowsy, or difficult to rouse? Note any agitation, hypervigilance, or reduced awareness. If the patient wakes with mild prompting and then remains alert throughout the assessment, score this as 0. Only score 4 if the abnormality persists — e.g. ongoing drowsiness, repeated drifting off, hyperalert/agitated behaviour, or unresponsiveness. This single item carries the highest weighting (4 points) because altered alertness is a hallmark of delirium.

For the AMT4, ask the four questions in sequence: “Can you tell me your age? Your date of birth? Where we are right now? What year is it?” Score each error. For months backward, instruct the patient clearly: “Can you tell me the months of the year in reverse order, starting with December?” Count the number of months correctly recited in reverse before the first error. If the patient refuses or cannot attempt the task, score as untestable (2). These items detect cognitive impairment whether from delirium, dementia, or both.

This item asks whether there has been a significant change or fluctuation in mental function over the preceding two weeks, still evident in the last 24 hours. Sources of evidence include: nursing observations (e.g. “the patient was confused overnight but fine this morning”), family reports (“she’s not been herself since Tuesday”), and clinical records. If no informant is available and the clinical record is insufficient, this item may be difficult to score — err on the side of scoring “Yes” if there is any clinical suspicion of acute change.

Score 0: Delirium is unlikely at this point. Document the assessment. Consider reassessing if clinical concern develops later — delirium can emerge at any time during an admission.

Score 1–3: Cognitive impairment is present. Consider whether this is known or new. If new, arrange formal cognitive assessment (e.g. MoCA, ACE-III) and consider referral to a memory service if the pattern suggests dementia. Reassess for delirium if any acute change is subsequently noted.

Score ≥4: Possible delirium. Initiate the delirium workup (bloods, urinalysis, imaging as indicated), review medications, address precipitants, implement non-pharmacological delirium interventions (reorientation, sleep hygiene, mobilisation, hydration, sensory aids), and consider specialist referral if the delirium does not resolve with treatment of identified causes.