Trends in Diagnosis Related Groups for Inpatient Admissions and Associated Changes in Payment From 2012 to 2016

Importance Hospitals are reimbursed based on Diagnosis Related Groups (DRGs), which are defined, in part, by patients having 1 or more complications or comorbidities within a given DRG family. Hospitals have made substantial investment in efforts to document these complications and comorbidities. Objective To examine temporal trends in DRGs with a major complication or comorbidity, compare these findings with 2 alternative measures of disease severity, and estimate associated changes in payment. Design, Setting, and Participants This retrospective cohort study used data from the all-payer National Inpatient Sample for admissions assigned to 1 of the top 20 reimbursed DRG families at US acute care hospitals from January 1, 2012, to December 31, 2016. Data were analyzed from July 10, 2018, to May 29, 2019. Exposures Quarter year of hospitalization. Main Outcomes and Measures The primary outcome was the proportion of DRGs with a major complication or comorbidity. Secondary outcomes were comorbidity scores, risk-adjusted mortality rates, and estimated payment. Changes in assigned DRGs, comorbidity scores, and risk-adjusted mortality rates were analyzed by linear regression. Payment changes were estimated for each DRG by calculating the Centers for Medicare & Medicaid Services weighted payment using 2012 and 2016 case mix and hospitalization counts. Results Between 2012 and 2016, there were 62 167 976 hospitalizations for the 20 highest-reimbursed DRG families; the sample was 32.9% male and 66.8% White, with a median age of 57 years (interquartile range, 31-73 years). Within 15 of these DRG families (75%), the proportion of DRGs with a major complication or comorbidity increased significantly over time. Over the same period, comorbidity scores were largely stable, with a decrease in 6 DRG families (30%), no change in 10 (50%), and an increase in 4 (20%). Among 19 DRG families with a calculable mortality rate, the risk-adjusted mortality rate significantly decreased in 8 (42%), did not change in 9 (47%), and increased in 2 (11%). The observed DRG shifts were associated with at least $1.2 billion in increased payment. Conclusions and Relevance In this cohort study, between 2012 and 2016, the proportion of admissions assigned to a DRG with major complication or comorbidity increased for 15 of the top 20 reimbursed DRG families. This change was not accompanied by commensurate increases in disease severity but was associated with increased payment. This cohort study evaluates trends in Diagnosis Related Groups with a major complication or comorbidity and estimates associated changes in payment. Question Have the proportion of inpatient admissions assigned to a Diagnosis Related Group (DRG) with major complication or comorbidity and the associated payments changed over time? Findings In this cohort study of US hospitalizations from 2012 to 2016, the proportion of DRGs with major complication or comorbidity increased for 15 of the top 20 reimbursed DRG families; however, commensurate increases in comorbidity burden or risk-adjusted mortality were not observed. These DRG shifts were associated with at least $1.2 billion in increased payment. Meaning In this study, trends in assigned DRGs did not reflect trends in the underlying case mix.