Background: 

International Classification of Diseases, 10th revision Z codes capture social needs related to health care encounters and may identify elevated risk of acute care use.

Objectives: 

To examine associations between Z code assignment and subsequent acute care use and explore associations between social need category and acute care use.

Research Design: 

Retrospective cohort study.

Subjects: 

Adults continuously enrolled in a commercial or Medicare Advantage plan for ≥15 months (12-month baseline, 3–48 month follow-up).

Outcomes: 

All-cause emergency department (ED) visits and inpatient admissions during study follow-up.

Results: 

There were 352,280 patients with any assigned Z codes and 704,560 sampled controls with no Z codes. Among patients with commercial plans, Z code assignment was associated with a 26% higher rate of ED visits [adjusted incidence rate ratio (aIRR) 1.26, 95% CI: 1.25–1.27] and 42% higher rate of inpatient admissions (aIRR 1.42, 95% CI: 1.39–1.44) during follow-up. Among patients with Medicare Advantage plans, Z code assignment was associated with 42% (aIRR 1.42, 95% CI: 1.40–1.43) and 28% (aIRR 1.28, 95% CI: 1.26–1.30) higher rates of ED visits and inpatient admissions, respectively. Within the Z code group, relative to community/social codes, socioeconomic Z codes were associated with higher rates of inpatient admissions (commercial: aIRR 1.10, 95% CI: 1.06–1.14; Medicare Advantage: aIRR 1.24, 95% CI 1.20–1.27), and environmental Z codes were associated with lower rates of both primary outcomes.

Conclusions: 

Z code assignment was independently associated with higher subsequent emergency and inpatient utilization. Findings suggest Z codes’ potential utility for risk prediction and efforts targeting avoidable utilization.