Undiagnosed delirium is frequent and difficult to predict: Results from a prevalence survey of a tertiary hospital

Aims and objectives To study the prevalence and determinants of undiagnosed delirium in a tertiary hospital. Background Delirium is a common inpatient condition. It is frequently undiagnosed in a variety of settings, but determinants of undiagnosed delirium are largely unknown, and the frequency of undiagnosed delirium across all inpatient units is uncertain. The utility of hospital‐wide screening then is also uncertain. Methods Hospital‐wide prevalence study conducted over 4 months, using a chart‐based method. Gender, age, admitting unit, history of dementia and comorbidity were used in univariate and multivariate analyses to search for differences in patients with no delirium, with undiagnosed delirium and with diagnosed delirium. Sensitivity, specificity and number needed to screen were calculated from proportions in each group. Study was conducted in concordance with STROBE guidelines. Results Delirium was prevalent in 12.5% of all patients and undiagnosed in 24.1% of patients. Only age ≥65 years and a history of dementia predicted delirium, and undiagnosed delirium in both univariate and multivariate analyses. Age ≥65 years accounts for 92.3% sensitivity and 50.8% specificity for undiagnosed delirium in this group. History of dementia had a 23.0% sensitivity and 97.0% specificity. Twenty‐eight patients would need to be screened to detect a case of undiagnosed delirium. Discussion There was a high rate of delirium and undiagnosed delirium in this cohort. Known risk factors for delirium also independently predict undiagnosed delirium; other factors were not found. Conclusion Undiagnosed delirium is common and difficult to predict from patient baseline characteristics other than age. Relevance to clinical practice Assessment of all inpatients for delirium is recommended.