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Delirium, a serious neuropsychiatric hospitalization complication, is a manifestation of underlying neurocognitive vulnerability rather than an acute event. In Japan, a nationwide medical policy mandates early hospital-wide delirium risk screening to evaluate predefined risk factors in inpatient populations. We aimed to identify demographic and clinical factors independently associated with referral-based, consultation-confirmed delirium.

We conducted a retrospective observational study of consecutive hospitalized patients at Nara Medical University Hospital between June 2022 and November 2023, without exclusion criteria. Delirium risk factors were assessed within 3 days of admission using a standardized checklist based on national criteria. Delirium was diagnosed following specialist consultation according to the International Classification of Diseases, 10th Revision (ICD-10), and the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision criteria. Logistic regression analyses were performed to identify independent association with consultation-confirmed delirium.

Among 20,980 patients (mean age, 67.1 ± 17.0 years; males, 55.0%), 209 (1.0%) were diagnosed with delirium following specialist consultation. Overall, 56.4% met at least one predefined risk criterion at admission. In multivariable analyses adjusted for age and sex, dementia (odds ratio [OR], 3.995; 95% confidence interval [CI], 2.647-6.029), history of delirium (OR, 3.649; 95% CI, 2.158-6.170), and heavy alcohol use (OR, 1.648; 95% CI, 1.002-2.710) were independently associated with consultation-confirmed delirium.

In this large cohort evaluated under a nationwide screening framework, consultation-confirmed delirium was independently associated with baseline neurocognitive vulnerability (dementia and history of delirium) and heavy alcohol use, rather than chronological age alone, supporting vulnerability-focused risk stratification in routine clinical practice.