[Pitfalls in the diagnosis of delirium].

Background: The diagnosis of delirium is challenging and requires precise definitions in both clinical routine and in studies.

Aim: To point out various pitfalls in the clinical diagnosis of delirium and discuss solutions.

Methods: Review.

Results: Common problems include (a) clinical judgment of staff vs. the use of valid assessment tools, (b) different lists of criteria for delirium that may consider the symptoms of delirium differently and thus lead to inclusion or exclusion of patients, (c) different assessment tools that test the symptoms of delirium to different extents and thus have different accuracy, (d) patients with limited communication abilities, such as aphasia, where common tests often fail and alternative procedures may be more effective; (e) the decision whether to test delirium once, twice, three times, or more frequently in 24 h has consequences on the incidence and duration of delirium, (f) the end of delirium, often defined retrospectively as a delirium-free interval or prospectively as the time of transfer or occurrence of an exclusion criterion, can lead to considerable measurement inaccuracies.

Conclusions: Although not all problems can be definitively answered, transparent definition, performance, and documentation of diagnostic procedures are recommended.