Delirium Screening Instruments
The routine screening for delirium is recommended for all older people seen in clinical practice. As supported by the National Institute for Health and Care Excellence (NICE), the first step in the clinical assessment conducted in acute medical setting is to rule out delirium (i.e., “think delirium”), which is an essential step prior to conducting further clinical assessments in relation to cognition and/or genuine mental health problems . To date, several brief bedside instruments, most requiring professional training, have been developed to improve delirium recognition though only a handful have been properly evaluated for use in clinical setting
. Furthermore, there has been an emphasis on evaluation in hospital rather than community residential settings.
Recommended Delirium Screening Instruments
The two most widely recommended delirium screening tools are the Confusion Assessment Method (CAM; ) and the 4AT . Both tools take little time to complete and are easy to administer in clinical practice.
Confusion Assessment Method (CAM)  The Confusion Assessment Method (CAM) is one of the most widely used delirium screening instruments currently used in routine clinical practice. This instrument has also been adapted for use in the intensive care setting (i.e., CAM-ICU), thus allowing assessment of an individual who is unable to communicate verbally, e.g., critically ill patients on or off the ventilator.
The CAM diagnostic algorithm consists of four components: (1) acute onset of mental status changes of fluctuating course, (2) inattention, (3) disorganized thinking, and (4) an altered level of consciousness. The diagnosis of delirium is based on the presence of both components (1) and (2) and either (3) or (4). Based on the assessment, a patient is evaluated as CAM “positive” or “negative.”
A recent review, based on evaluation of 22 studies, and a total of 2442 patients, reported high sensitivity [82 % (95 % CI: 69-91 %)] and specificity [99 % (95 % CI: 87-100 %)] for CAM, with similar values for CAM-ICU, e.g., sensitivity 81 % (95 % CI: 57-93 %) and 98 % (95 % CI: 86-100 %) specificity , suggesting that even in trained hands, the diagnosis of delirium can be missed in up to one in every five cases if only using unimodal assessment in the form of the CAM or CAM- ICU. The relatively low sensitivity of both CAM and CAM-ICU was further highlighted by a more recent study that reported CAM sensitivity was as low as 27 % when used in the context of postoperative delirium in older people (>70 years), further arguing that the use of the CAM needs to be supported by detailed clinical assessment, based on the established delirium criteria (e.g., DSM-IV; ). In addition, the use of both CAM and CAM-ICU requires adequate professional training as supported by one study that found a decrease in sensitivity of 40 % when utilized by untrained staff . Lastly, studies suggest that there exists variation in the application of CAM with false negatives of delirium as high as 33 % when administered by nursing staff at the bedside .
4AT The “four As test” (4AT) was designed to be used in people even with severe drowsiness or agitation where cognitive testing and/or interview may not be possible . It provides a rapid assessment (takes less than 2 min to administer) and does not require special training. The test consists of four items on a maximum 12-point scale that assesses for alertness (Item 1), cognition in terms of a brief global assessment of cognition and attention using the four-item Abbreviated Mental Test (AMT-4) (Item 2) and “Month Backwards” (Item 3), and an acute change or fluctuation in mental status (Item 4). A score of 4 or above indicates possible delirium and/or cognitive impairment, while a score of 1-3 indicates possible cognitive impairment and a score of 0 indicates delirium, and severe cognitive impairment are unlikely, though this interpretation is subject to the score of Item 4.
The 4AT had a sensitivity of 89.7 % and specificity 84.1 % for delirium against the DSM-IV-TR criteria , whereas a recent study conducted in patients with an acute stroke found the 4AT test to have the highest sensitivity (100 %) and a reasonable specificity (82 %) for detecting delirium in comparison to other delirium tests, including the CAM . As the test also includes the Abbreviated Mental Test and Month Backwards, which are both validated short tests for cognitive impairment, it is not surprising that the 4AT also has a reasonable sensitivity (86 %) and specificity (78 %) to detect cognitive impairment  . Use of the 4AT as a screening tool seems promising; however, further work is necessary to evaluate the usability of 4AT when undertaken by nonmedical (i.e., nursing) professionals.