Educational scope notice: This is a study note for medical students, not medical advice, diagnosis, or treatment guidance. Clinical management should follow local protocols and current guidelines.
The first diagnostic step is suspecting delirium at all. Up to two-thirds of cases are missed, partly because nobody looks and partly because hypoactive delirium stays quiet. Suspicion should be routine in elderly, post-surgical, and critically ill patients, and the history must come largely from family or carers, since the patient cannot report reliably. The questions that matter are whether mentation fell abruptly, whether it fluctuates, what systemic illness worsened, which drugs were started or stopped, and whether even minor head trauma, common and easily forgotten in the elderly, intervened.
Early clues include an inability to perform in the usual manner, fading awareness, insomnia, fearfulness, and vivid dreams. On examination, attention and arousability come first: a general behavioural assessment of whether the patient attends and stays awake, before any detailed testing of orientation, recent memory, language, or hallucinations. Attentional failure often precedes whatever the formal mental status examination later confirms.
The Confusion Assessment Method
The Confusion Assessment Method (CAM) compresses the syndrome into four observable features so a fluctuating, sleepy, or agitated patient can be screened in minutes:
| Feature | Description |
|---|---|
| Feature 1 | Acute onset with fluctuating course |
| Feature 2 | Inattention |
| Feature 3 | Disorganised thinking |
| Feature 4 | Altered level of consciousness |
The rule is features 1 and 2 plus either 3 or 4. All four are not required: disorganised thinking alone or an altered level of consciousness alone completes the triad. In its original validation the CAM reached sensitivity around 94–100% with specificity around 90–95% and strong agreement between observers.
Routine assessment in current UK guidance runs on the 4AT, with CAM-ICU or the Intensive Care Delirium Screening Checklist in critical care and post-surgical recovery, and the final diagnosis rests with a clinician with relevant expertise. CAM remains the taught bedside rule because it shows the reasoning plainly, not because it is the current front-door instrument everywhere.
CAM beside the formal DSM-5 framework
DSM-5 defines delirium formally: a disturbance in attention and awareness that develops acutely and fluctuates, accompanied by another cognitive disturbance, not better explained by another neurocognitive disorder or by coma, with evidence from history, examination, or investigations of a medical, substance, medication, toxin, or multiple-cause aetiology. The plain-English version is that DSM-5 says what delirium is, while CAM is the quick way to catch it at the bedside.
Each CAM feature maps onto part of that definition. Acute onset with fluctuation matches the DSM-5 tempo requirement. Inattention captures the central attentional disturbance. Disorganised thinking captures part of the additional cognitive disturbance, and altered level of consciousness captures the awareness and arousal side. On the arousal side the inclusive reading applies: non-comatose impaired arousal, from drowsiness through stupor or agitation, counts as inattention, since only coma sits outside delirium. What CAM does not do is the diagnostic thinking DSM-5 additionally demands: confirming a change from baseline, excluding dementia or coma as the better explanation, and establishing an underlying cause. CAM positivity strongly supports delirium, but the search for the cause still follows.
When delirium, dementia, or delirium superimposed on dementia cannot be distinguished, the rule is to manage the delirium first.
Factors that predispose and precipitate
Four factors independently predispose to delirium: visual impairment, severe illness, pre-existing cognitive impairment or dementia, and dehydration, signalled by a raised blood urea-to-creatinine ratio and common in elderly inpatients. The wider background list includes age, fluid and electrolyte disturbance, hepatic failure and other metabolic illness, infection, malnutrition, stroke, sensory impairment or deprivation, sleep disturbance, fever and hypothermia, alcohol or sedative dependence, fractures (femoral fracture is a classic), depression, and medication changes. Environmental upheaval, such as a move to a new ward, can precipitate delirium in a frail patient. Cardiac, thoracic, cataract, and urological surgery carry particular risk.
Five factors independently precipitate delirium once the patient is admitted: physical restraints, malnutrition, bladder catheters, three or more drugs given within 24 hours, and iatrogenic complications. Each of these is a direct invitation to prevention: fewer restraints and catheters, fed and hydrated patients, and fewer simultaneous prescriptions.
This four-plus-five schema is classic Inouye teaching rather than the current NICE list, which names age over 65, cognitive impairment or dementia, hip fracture, and severe illness. Both lists point the same way: the frail, ill, medicated, and sensorily deprived patient is the one to watch.
Evidence anchors
- Inouye SK, et al. Clarifying confusion: the Confusion Assessment Method: https://pubmed.ncbi.nlm.nih.gov/2240918/
- NICE. Delirium: prevention, diagnosis and management (CG103): https://www.nice.org.uk/guidance/cg103
- European Delirium Association and American Delirium Society. DSM-5 criteria, level of arousal and delirium diagnosis: https://pmc.ncbi.nlm.nih.gov/articles/PMC4177077/