Comorbidity combinations in schizophrenia inpatients and their associations with service utilization: A medical record-based analysis using association rule mining

Background Comorbidities are common among patients with schizophrenia yet the prevalence of comorbidity combinations and their associations with inpatient service utilization and readmission have been scarcely explored. Methods Data were extracted from discharge summaries of patients whose primary diagnosis was schizophrenia spectrum disorders (ICD-10: F20-F29). We identified 30 most frequent comorbidities in patients’ secondary diagnoses and then used the association rule mining (ARM) method to derive comorbidity combinations associated with length of stay (LOS), daily expense and one-year readmission. Results The study included data from 8252 patients. The top five most common comorbidities were extrapyramidal syndrome (EPS, 44.58%), constipation (31.63%), common cold (21.80%), hyperlipidemia (20.99%) and tachycardia (19.13%). Most comorbidity combinations identified by ARM were significantly associated with longer LOS (≥70 days), few were associated with higher daily expenses, and fewer with readmission. The 3-way combination of common cold, hyperlipidemia and fatty liver had the strongest association with longer LOS (adjusted OR (aOR): 3.38, 95% CI: 2.12-5.38). The combination of EPS and mild cognitive disorder was associated with higher daily expense (≥700 RMB) (aOR: 1.67, 95% CI: 1.20-2.31). The combination of constipation, tachycardia and fatty liver were associated with higher 1-year readmission (aOR: 2.05, 95% CI: 1.03-4.09). Conclusion EPS, constipation, and tachycardia were among the most commonly reported comorbidities in schizophrenia patients in Beijing, China. Specific groups of comorbidities may contribute to higher inpatient psychiatric service utilization and readmission. The mechanism behind the associations and potential interventions to optimize service use warrant further investigation.