14th February 2025

Investigations in delirium

Brief cognitive assessments such as the 4AT or short Confusion Assessment Method (CAM) can be used to support the diagnosis, although abnormal results are not specific to delirium, and differentiating delirium from dementia (or delirium-on-dementia) can be challenging. A collateral history is particularly crucial, and also more specific tests such as the Observational Scale of Level of Arousal (over 80% specific).

After a diagnosis of delirium is made, further investigation is needed for any underlying cause. There is a wide differential diagnosis for confusion, which can be found in the Dementia section (see Presentation and diagnosis of dementia). Although an acute condition is more likely in delirium, long-term comorbidities and medications should also be reviewed.

General blood tests (including bone profile, TFTs, B12, folate) and a septic screen are usually performed. CT brain and ECG should be considered. Context-specific investigations may include:

• Drug levels for patients on digoxin, lithium or quinidine
• LP or EEG if suspecting meningitis, seizure activity or encephalopathy
• Urine drug screen