Comparison of Methods to Define High Use of Inpatient Services Using Population-Based Data

As healthcare system use and costs continue to rise, increased importance has been placed on identifying the small subgroup of patients that drive this trend.¹ It is estimated that 5% of healthcare users account for over 60% of healthcare spending.^2-6 Furthermore, care for these “high users” is expensive due to an over-reliance on inpatient services. Approximately 40% of all health spending is for inpatient care, the largest single category of health spending, which is similarly skewed toward high users.^1,3,5 Improving our understanding of this population may provide an opportunity to direct improvement efforts to a select group of patients with a potentially high benefit, as well as move care away from the costly inpatient setting.

However, the development of effective interventions to improve patient experience and outcomes while decreasing costs (referred to as the “Triple Aim” by the Institute for Health Improvement) for high users of inpatient services hinges on the methodology used to identify this high-risk population.⁷ There is substantial variability in definitions of high users; the most common definitions are based on the number of hospital encounters, days spent in the hospital, and hospital costs.^8-15 Definitions have intrinsic differences in their implications around appropriateness, efficiency, and financial sustainability of inpatient resource use. Though the constructs underlying these definitions are highly variable, direct comparisons of differences in patient capture are limited.

A recent study from a single US center explored the clinical characteristics of hospital patients based on definitions of use vs cost and observed important differences in patients’ profiles and outcomes.¹² While this suggests that the choice of definition may have major implications for whom to target (and the efficacy of any proposed interventions), this concept has not been explored at the population level. Therefore, we used population-based administrative data from a single-payer healthcare system to compare 3 common definitions of high inpatient service use and their influence on patient capture, health outcomes, and inpatient system burden.

Data Sources and Study Population

We conducted a retrospective population-based study using administrative and clinical data for the province of Alberta, including the discharge abstracts database, physician claims, ambulatory care records, population health registry file, and aggregated data from the Canadian census.¹⁶ We identified all adults who had 1 or more hospitalizations with a discharge date between April 1, 2012, and March 31, 2013, though the admission date could be prior to April 1, 2012.

Definition of High-Inpatient Use

High-inpatient use was defined using 3 metrics: number of inpatient episodes, length of stay, and cost. As in prior studies, for each definition, individuals in the upper5th percentile of the relevant distribution were designated “high users,”^2,15 while patients in the lower 95th percentile were considered “nonhigh users.” Patients could be defined as a high user in more than 1 definition.

Patients with 3 or more hospital episodes were defined as high users for the “number of inpatient episodes” definition. A hospital episode of care was defined as an event that resulted in discharge (or death) from an inpatient facility. If an individual was admitted to a hospital and transferred to another facility within 1 day of discharge, the hospitalizations were considered part of the same episode of care.

The “length of stay” definition refers to the cumulative number of days spent in an inpatient facility for all eligible episodes of care. Patients with 56 or more days in hospital during the study period were considered high users. Day of admission and discharge were considered full inpatient days, regardless of the time of admission and discharge.

The “cost” definition considered the cumulative estimated cost of every eligible episode of care. We estimated costs for each hospitalization using resource intensity weights (RIW). This is a relative weighted value for the average inpatient case after taking factors such as age, comorbidity, and procedures into account. The RIW for each episode was multiplied by the national average inpatient cost.¹⁷ Based on this definition, patients with a cumulative hospital cost of ≥ $63,597 were deemed high users. All costs were calculated in Canadian Dollars (CAD, $) and adjusted to 2013 dollars based on Statistics Canada’s Consumer Price Index.¹⁸