Which indicator is considered hallmark for diagnosing delirium?

The hallmark indicator for diagnosing delirium is an acute change in level of arousal. Delirium is often characterized by a sudden onset of confusion, fluctuating levels of consciousness, and disturbances in attention. This acute change can manifest as either hyperactive (increased arousal) or hypoactive (decreased arousal) states, making it a critical feature for establishing a diagnosis.

In contrast, stable levels of arousal do not indicate delirium; rather, they suggest cognitive functioning is steady, which is the opposite of what is observed in delirium. Inconsistent mood changes might occur in various psychiatric conditions and may be seen in delirium as well, but they are not specific enough to serve as a primary diagnostic marker. Chronic confusion indicates long-standing cognitive impairment, such as that seen in dementia, rather than the sudden disturbances characteristic of delirium. Thus, the acute change in level of arousal directly aligns with the hallmark symptoms of delirium and is essential for appropriate diagnosis and subsequent management.