Several tools have been developed to screen for delirium symptoms among patients, and most have been designed to be administered by nursing staff. These may aid in the recognition of delirium, especially in nursing homes, where physician visits are less frequent. The number of delirium symptoms covered, the specificity of items for delirium, and the complexity of administration all vary. Screening instruments include the Clinical Assessment of Confusion–A (CAC-A) (32), the Confusion Rating Scale (CRS) (33), the MCV Nursing Delirium Rating Scale (MCV-NDRS) (34), and the NEECHAM Confusion Scale (35).

Investigators have designed a variety of instruments to make a formal diagnosis of delirium. These instruments consist of operationalized delirium criteria from a variety of diagnostic systems, often in the form of a checklist incorporating information from patient observation and the medical record (e.g., DSM-III-R, DSM-IV, ICD-9, and ICD-10). The rate of delirium diagnosis obtained by using these diagnostic instruments varies according to both the diagnostic system that was used and the particular way in which the authors chose to operationalize the criteria. One structured diagnostic interview schedule, the Delirium Symptom Interview (DSI), can be administered by lay interviewers and used in epidemiological studies (36). Other delirium diagnostic instruments include the Confusion Assessment Method (CAM) (37), Delirium Scale (Dscale) (38), Global Accessibility Rating Scale (GARS) (39), Organic Brain Syndrome Scale (OBS) (40), and Saskatoon Delirium Checklist (SDC) (41).

Several instruments have been developed to rate the severity of delirium symptoms. Ratings are generally based both on behavioral symptoms and on confusion and cognitive impairment. Rating the severity of delirium over time may be useful for monitoring the effect of an intervention or plotting the course of a delirium over time. These scales have also been used to make the diagnosis of delirium by considering patients with scores above a specified cutoff to have the diagnosis. Such rating scales include the Delirium Rating Scale (DRS) (42) and the Memorial Delirium Assessment Scale (MDAS) (43).

Several laboratory evaluations have been investigated for possible use in evaluating delirium. With the exception of the EEG, these tests are experimental and currently appropriate only for research purposes. For several decades, investigators have observed EEG changes in patients with delirium (44). EEG changes consist mainly of generalized slowing, although low-voltage fast activity is seen in some types of delirium, such as delirium tremens (45). The presence of EEG abnormalities has fairly good sensitivity for delirium (in one study, the sensitivity was found to be 75%), but their absence does not rule out the diagnosis; thus, the EEG is no substitute for careful clinical observation. Among the experimental laboratory tests that have been investigated for use in delirium, those that appear to show some promise include brain imaging (46, 47) and measures of serum anticholinergic activity (48).