Comparison of hospital risk-standardized mortality rates calculated by using in-hospital and 30-day models: an observational study with implications for hospital profiling

Abstract

Background: In-hospital mortality measures, which are widely used to assess hospital quality, are not based on a standardized follow-up period and may systematically favor hospitals with shorter lengths of stay (LOSs).

Objective: To assess the agreement between performance measures of U.S. hospitals by using risk-standardized in-hospital and 30-day mortality rates.

Design: Observational study.

Setting: Nonfederal acute care hospitals in the United States with at least 30 admissions for acute myocardial infarction (AMI), heart failure (HF), and pneumonia from 2004 to 2006.

Patients: Medicare fee-for-service patients admitted for AMI, HF, or pneumonia from 2004 to 2006.

Measurements: The primary outcomes were in-hospital and 30-day risk-standardized mortality rates (RSMRs).

Results: Included patients comprised 718,508 admissions to 3135 hospitals for AMI, 1,315,845 admissions to 4209 hospitals for HF, and 1,415,237 admissions to 4498 hospitals for pneumonia. The hospital-level mean patient LOS varied across hospitals for each condition, ranging from 2.3 to 13.7 days for AMI, 3.5 to 11.9 days for HF, and 3.8 to 14.8 days for pneumonia. The mean RSMR differences (30-day RSMR minus in-hospital RSMR) were 5.3% (SD, 1.3) for AMI, 6.0% (SD, 1.3) for HF, and 5.7% (SD, 1.4) for pneumonia; distributions varied widely across hospitals. Performance classifications differed between the in-hospital and 30-day models for 257 hospitals (8.2%) for AMI, 456 (10.8%) for HF, and 662 (14.7%) for pneumonia. Hospital mean LOS was positively correlated with in-hospital RSMRs for all 3 conditions.

Limitation: Medicare claims data were used for risk adjustment.

Conclusion: In-hospital mortality measures provide a different assessment of hospital performance than 30-day mortality and are biased in favor of hospitals with shorter LOSs.

Primary funding source: The Centers for Medicare & Medicaid Services and National Heart, Lung, and Blood Institute.

Figure 1

Figure 1a. Acute Myocardial Infarction Hospital Mean Length of Stay Figure 1b: Heart Failure Hospital Mean Length of Stay Figure 1c: Pneumonia Hospital Mean Length of Stay

Figure 2

Figure 2a: Distribution of (30-Day) – (In-hospital) Risk Standardized Mortality Rates for Acute Myocardial Infarction Figure 2b: Distribution of (30-Day) – (In-hospital) Risk Standardized Mortality Rates for Heart Failure Figure 2c: Distribution of (30-day) – (In-hospital) Risk Standardized Mortality Rates for Pneumonia