Trends in Health Service Utilization After Enrollment in an Interdisciplinary Primary Care Clinic for Veterans with Addiction, Social Determinants of Health, or Other Vulnerabilities

BACKGROUND: Models of interdisciplinary primary care (IPC) may improve upon traditional primary care approaches in addressing addiction and social determinants of health. OBJECTIVE: To compare the trends in health care utilization in the year before and after enrollment in an IPC clinic model, and explore the variations in temporal patterns for patients with histories of high emergency department (ED) use, homelessness, and/or substance use disorders (SUDs). DESIGN AND PARTICIPANTS: Interrupted time series study of utilization among IPC patients. MAIN MEASURES: Quarterly ED, inpatient, primary care, and behavioral health visits were abstracted from administrative data before and after IPC enrollment. Negative binomial segmented regressions estimated changes in health care utilization over time. We used interactions to test for statistical differences in temporal patterns for IPC subgroups. RESULTS: Among IPC patients (n=994), enrollment was associated with overall reductions in ED, inpatient, and behavioral health visits (p’s<0.001) and increases in primary care (p’s<0.001). Temporal patterns of ED visits, hospitalizations, and behavioral health differed across IPC subgroups (interaction p’s<0.001). For those with histories of high ED use (n=265), ED, inpatient, and behavioral health visits decreased after enrollment (level change incidence rate ratios [IRRs]=0.57–0.69) and continued to decline over time (post-enrollment IRRs=0.80–0.88). Among other patients with homeless experiences (n=123), there were initial declines in hospitalizations (IRR=0.33) and overall declines in behavioral health visits (level change and post-enrollment IRRs=0.46–0.94). Other patients with SUDs had initial declines in hospitalizations (IRR=0.46), and post-enrollment declines in rates of specialty SUD visits (IRR=0.92). For all patients, primary care visits initially increased (level change IIRs=2.47–1.34) then gradually declined (post-enrollment IRRs=0.92–0.92). CONCLUSIONS: An IPC model of care reduces acute care and behavioral health service use, particularly for patients with historically high ED use. IPC models may improve patient and system outcomes of vulnerable patient populations with social, clinical, and addiction morbidities.