A formal delirium assessment can be lengthy, and its results are prone to subjectivity. Wong and colleagues conducted a systematic review to determine the accuracy of several instruments in diagnosing delirium in adults.

A total of 25 studies met the inclusion criteria. They included 26 to 791 participants, for a total of 3,027, and 11 bedside delirium instruments with corresponding diagnostic accuracy data. The instruments were the Global Attentiveness Rating (GAR), Memorial Delirium Assessment Scale (MDAS), Confusion Assessment Method (CAM), Delirium Rating Scale (DRS), Delirium Rating Scale Revised-98 (DRS-R-98), Clinical Assessment of Confusion (CAC), Delirium Observation Screening Scale (DOSS), Mini-Mental State Examination (MMSE), Nursing Delirium Screening Scale (Nu-DESC), Digit Span Test, and Vigilance "A" Test.

Delirium was prevalent in 9% to 63% of study patients. Positive results on the GAR, MDAS, CAM, DRS-R-98, CAC, and DOSS suggested delirium (likelihood ratios greater than 5). Negative results on the GAR, MDAS, CAM, DRS-R-98, DRS, DOSS, Nu-DESC, and MMSE suggested that delirium was less likely (likelihood ratios of 0.2 or less). The MMSE was found to be the least useful instrument, the GAR was assessed in only one study and may be accurate only in geriatric patients, and the Digit Span Test and Vigilance "A" Test were ineffective when used in isolation.

The authors state that although several instruments tested were sensitive, specific, rapid, and simple, the CAM, in particular, was found to be accurate and can be administered in five minutes.