F05 — Delirium, not induced by alcohol and other psychoactive substances

Concept, in one sentence

An acute, fluctuating disturbance of consciousness and attention, usually with an identifiable and often reversible physical cause.

Decisive boundary cues

• Acute onset, hours to days -> weighs toward F05 over F00-F03's gradual course.
• Marked within-day fluctuation -> weighs toward F05 over a stable dementia picture.
• Disturbed consciousness/attention at assessment -> weighs toward F05 over F06/F07, where consciousness is clear.

Duration/course cue

Acute onset (hours to days) with fluctuation over the course of a day; usually resolves once the underlying cause is treated.

Nearest alternatives

F00, F03, F06

Common mistake

Assuming an acutely confused older adult is 'just confused because of their age or dementia' without checking for acuity, fluctuation, and an underlying medical cause.

Retrieval prompt — one-line memory anchor

What single question would you ask first to check whether this is delirium rather than dementia?