1. Think in terms of vulnerability and triggers

A delirium assessment has two linked questions:

1. Does this person have delirium?
2. What may have caused, triggered, or prolonged it?

A tool such as the 4AT helps detect possible delirium. It does not identify the cause. The final diagnosis and cause assessment remain clinical.

Some people have greater background vulnerability because of dementia, frailty, severe illness, multimorbidity, or sensory impairment. They may develop delirium after a relatively modest acute disturbance. A person with less vulnerability may require a more severe disturbance. Age, dementia, or frailty can therefore affect risk, but none is an adequate explanation for a new acute change.

Possible acute contributors include infection or another acute illness, hypoxia, circulatory or metabolic disturbance, medication effects, a recent operation or procedure, pain, dehydration, urinary retention, constipation, immobility, sleep disruption, and an unfamiliar care environment. Several may coexist (Ormseth et al. 2023).

In practice, causation is not always certain. Record a finding as a possible contributor unless the evidence supports a more definite conclusion. A plausible explanation should guide action without closing the search too early.

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2. Check for clinical instability first

Delirium may be the first sign of serious acute illness. Before working through a cause list, decide whether the person is clinically unstable or deteriorating.

Use the emergency assessment and escalation process for your setting if there are concerns such as:

• a problem with airway, breathing, or circulation;
• new marked hypoxaemia, hypotension, or other abnormal physiological observations;
• markedly reduced consciousness or rapid deterioration;
• suspected sepsis;
• a new focal neurological deficit, seizure, or recent head injury; or
• concern about poisoning, intoxication, or withdrawal.

Complete the immediate bedside assessment and physiological observations required by the local deterioration pathway. Begin urgent treatment and call for the appropriate clinical help. Cause-finding, collateral history, and delirium assessment can continue alongside this care when it is safe to do so.

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3. Make a structured sweep

Once immediate threats are being addressed, use the same broad sweep each time. Adapt it to the person and setting.

• Acute illness and physiology: consider infection, hypoxia, cardiorespiratory illness, dehydration, bleeding, and disturbances of glucose, electrolytes, renal function, or other physiology.
• Brain events and injury: consider stroke, seizure and the period after a seizure, intracranial disease, and head injury when the history or findings suggest them.
• Medicines and substances: check recent starts, dose changes, omitted or stopped medicines, adverse effects, interactions, and the cumulative burden of medicines with anticholinergic effects (which can impair memory, attention, bladder and bowel function) or sedative effects (which can reduce alertness). Include prescribed, non-prescribed, and as-required medicines, and what was actually administered (Reisinger et al. 2023; Ieong et al. 2024).
• Pain and physical needs: look for pain, urinary retention, constipation, thirst, poor intake, immobility, pressure-related discomfort, and another source of unexpressed distress.
• Function, senses, sleep, and environment: check hearing and vision, mobility, sleep interruption, changes of room or care setting, unfamiliar routines, and barriers to communication.

This is a framework, not a claim that every item is present or equally likely. The timing, examination, and other evidence determine what deserves priority.

Mnemonics such as PINCH ME can be useful memory prompts. They are not complete cause lists, diagnostic tools, or substitutes for clinical assessment.

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4. Find evidence for possible contributors

Talk with the person

Ask about new symptoms and about pain, breathlessness, thirst, nausea, bowel and bladder problems, sleep, fear, and recent events. Use short questions, hearing or language support, and enough time for a response. A person with severe inattention or drowsiness may not be able to give a reliable history, but should still be included as far as possible.

Establish baseline and recent course

Ask family, carers, familiar staff, or another person who knows the patient about usual cognition and function, the onset and fluctuation of the change, recent illness, falls, procedures, intake, bowel and bladder function, and changes in care setting. Check previous records when collateral information is not immediately available.

Review records and medicines

Look at observation charts, fluid and food intake, bowel and bladder records, recent procedures, falls, and the clinical course. Reconcile the medicine list with the administration record. Ask about recent prescriptions, dose changes, as-required doses, missed regular medicines, non-prescription products, and substance use. If a medicine may be contributing, ask the prescriber and pharmacist to review the balance of benefit and harm. Do not stop essential medicines outside your role or without considering withdrawal and the condition being treated (Weidmann et al. 2025).

Examine and observe

Use a focused but sufficiently broad physical and neurological examination, guided by the presentation. Observe breathing, movement, facial expression, guarding, swallowing, skin, and the person’s response to care. Consider hidden pain, retention, or constipation in a person who is quiet, drowsy, or unable to describe symptoms.

Select investigations to answer clinical questions

Investigations should follow the history, collateral information, observations, and examination. The tests needed will vary with the findings and care setting. Use current local guidance and choose bedside tests, blood tests, microbiology, imaging, or specialist assessment when each has a clinical indication. Review the results in context rather than treating an isolated abnormality as the explanation.

Current UKHSA and NHS England primary care guidance says not to perform urine dipsticks in adults over 65 because they are unreliable for ruling urinary tract infection in or out. Follow the urinary tract infection guidance for the person’s setting. Asymptomatic bacteriuria, meaning bacteria in the urine without symptoms or signs attributable to urinary tract infection, is common in older people. Bacteriuria or a positive culture alone does not establish symptomatic urinary tract infection or prove that it caused the delirium. If fever, unstable blood pressure or circulation, or concern about sepsis is present, assess urgently, look for all possible infection sources, and follow local infection and sepsis guidance. Do not infer a urinary source from bacteriuria alone (Stall et al. 2024).

5. Avoid common cause-finding traps

Stopping after the first finding. Pneumonia, a recent operation, or a medication change may be relevant, but another contributor can be present at the same time. Continue the sweep and review the response.

Treating an association as proof. A laboratory abnormality or positive culture may be incidental. Ask whether it fits the symptoms, examination, timing, and wider clinical picture.

Assuming a quiet person is comfortable or well. Hypoactive delirium can accompany severe illness, pain, thirst, urinary retention, constipation, or fear. Look, ask, and examine.

Using a delirium tool as a cause-finding tool. The 4AT detects possible delirium; it does not distinguish infection, medicine effects, pain, or other triggers.

Ordering the same tests for everyone. Indiscriminate testing can produce incidental findings and does not replace a clinical assessment. Tests should answer a question raised by the history or findings.

Writing “delirium due to infection” too early. State what is known, what is suspected, what has been done, and what still needs review. Update the assessment as evidence changes.

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7. Act, record, and look again

Do not wait for certainty before addressing a serious or readily remediable problem. Prioritise threats to life and safety, then manage likely contributors in parallel within the person’s overall goals of care. Continue orientation, communication, hydration, nutrition, pain assessment, mobility, sensory support, and sleep protection while cause-specific treatment proceeds.

Keep a current contributor list so staff across professions and shifts can see the reasoning:

Document more than “confused” or “delirium due to infection”. Record:

• the person’s usual cognitive and functional baseline and the source of that information;
• onset, fluctuation, and exact changes observed;
• clinical stability and any urgent escalation;
• possible contributors and the evidence for them;
• actions, named responsibility, response, and outstanding results; and
• the next review and what should trigger earlier escalation.

Delirium may take time to improve after treatment starts. If it persists, worsens, or follows an unexpected course, repeat the history, examination, medication review, and structured sweep. Check whether treatments were delivered and effective, whether a new problem has arisen, and whether the diagnosis needs reconsideration. Seek senior or specialist advice when the clinical picture remains unclear.

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