Utilization, Steering, and Spending in Vertical Relationships Between Physicians and Health Systems.

Importance: Vertical relationships (eg, ownership or affiliations, including joint contracting) between physicians and health systems are increasing in the US. Objective: To analyze how vertical relationships between primary care physicians (PCPs) and large health systems are associated with changes in ambulatory and acute care utilization, referral patterns, readmissions, and total medical spending for commercially insured individuals. Design, Setting, and Participants: This case-control study with a repeated cross-section, stacked event design analyzed outcomes of patients whose attributed PCP entered a vertical relationship with a large health care system in 2015 or 2017 compared with patients whose attributed PCP was either never or always in a vertical relationship with a large health system from 2013 to 2017 in the state of Massachusetts. The sample consisted of commercially insured patients who met enrollment criteria and who were attributed to PCPs who were included in the Massachusetts Provider Database in 2013, 2015, and 2017 and for whom vertical relationships were measured. Enrollee and claims data were obtained from the 2013 to 2017 Massachusetts All-Payer Claims Database. Statistical analyses were conducted between January 5, 2021, and June 5, 2023. Exposure: Evaluation-and-management visit with attributed PCP in 2015 to 2017. Main Outcomes and Measures: Outcomes (which were measured per patient-year [ie, per patient per year from January to December] in this sample) were utilization (count of specialist physician visits, emergency department [ED] visits, and hospitalizations overall and within attributed PCP's health system), spending (total medical expenditures and use of high-price hospitals), and readmissions (readmission rate and use of hospitals with a low readmission rate). Results: The sample of 4 030 224 observations included 2 147 303 females (53.3%) and 1 881 921 males (46.7%) with a mean (SD) age of 35.07 (19.95) years. Vertical relationships between PCPs and large health systems were associated with an increase of 0.69 (95% CI, 0.34-1.04; P < .001) in specialist visits per patient-year, a 22.64% increase vs the comparison group mean of 3.06 visits, and a $356.67 (95% CI, $77.16-$636.18; P = .01) increase in total medical expenditures per patient-year, a 6.26% increase vs the comparison group mean of $5700.07. Within the health care system of the attributed PCPs, the number of specialist visits changed by 0.80 (95% CI, 0.56-1.05) per patient year (P < .001), a 29.38% increase vs the comparison group mean of 2.73 specialist visits per patient-year. The number of ED visits changed by 0.02 (95% CI, 0.01-0.03) per patient year (P = .001), a 14.19% increase over the comparison group mean of 0.15 ED visits per patient-year. The number of hospitalizations changed by 0.01 (95% CI, 0.00-0.01) per patient-year (P < .001), a 22.36% increase over the comparison group mean of 0.03 hospitalizations per patient-year. There were no differences in readmission outcomes. Conclusions: Results of this case-control study suggest that vertical relationships between PCPs and large health systems were associated with steering of patients into health systems and increased spending on patient care, but no difference in readmissions was found.