Association between Substance Use Disorders and 30-Day Readmission among Patients with Schizophrenia: A Retrospective Cohort Study Using MIMIC-IV

Abstract

Background: Schizophrenia is frequently accompanied by substance use disorders, which complicate clinical management and contribute to recurrent hospitalisation. Evidence regarding the association between substance use disorders and 30-day hospital readmission remains inconsistent. Objective: To examine the association between substance use disorder (SUD) and 30-day hospital readmission among adults hospitalised with schizophrenia. Methods: This retrospective cohort study used version 3.1 of the Medical Information Mart for Intensive Care IV (MIMIC-IV). Adults with schizophrenia were identified using International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM), and Tenth Revision, Clinical Modification (ICD-10-CM), diagnosis codes. Substance use disorder was the primary exposure, and 30-day all-cause hospital readmission was the primary outcome. Multivariable logistic regression was used to estimate adjusted odds ratios (aORs) and 95% confidence intervals (CIs) after adjustment for age, sex, race or ethnicity, insurance type, Charlson Comorbidity Index, hospital length of stay, and discharge location. Results: A total of 7,968 eligible hospital admissions were included, of which 2,728 (34.2%) had substance use disorder and 2,461 (30.9%) experienced a 30-day readmission. After adjustment, substance use disorder was associated with lower odds of 30-day readmission (aOR, 0.85; 95% CI, 0.76 to 0.95; p = 0.004). Higher Charlson Comorbidity Index scores were associated with increased odds of readmission (aOR, 1.06; 95% CI, 1.03 to 1.09; p < 0.001), whereas discharge to a psychiatric facility was associated with markedly higher odds of readmission than discharge to home (aOR, 5.95; 95% CI, 4.72 to 7.50; p < 0.001). Conclusions: Substance use disorder was associated with lower adjusted odds of 30-day hospital readmission among adults hospitalised with schizophrenia. Patient characteristics, comorbidity burden, insurance type, and discharge destination were also associated with readmission, highlighting the importance of comprehensive discharge planning and continued follow-up. Additional multicentre studies are needed to examine clinical and social factors that may influence readmission after hospitalisation for schizophrenia.