Risk-adjusting acute myocardial infarction mortality: are APR-DRGs the right tool?

Health Serv Res. 2000 Mar;34(7):1469-89.


Objective: To determine if a widely used proprietary risk-adjustment system, APR-DRGs, misadjusts for severity of illness and misclassifies provider performance.

Data sources: (1) Discharge abstracts for 116,174 noninstitutionalized adults with acute myocardial infarction (AMI) admitted to nonfederal California hospitals in 1991-1993; (2) inpatient medical records for a stratified probability sample of 974 patients with AMIs admitted to 30 California hospitals between July 31, 1990 and May 31, 1991.

Study design: Using the 1991-1993 data set, we evaluated the predictive performance of APR-DRGs Version 12. Using the 1990/1991 validation sample, we assessed the effect of assigning APR-DRGs based on different sources of ICD-9-CM data.

Data collection/extraction methods: Trained, blinded coders reabstracted all ICD-9-CM diagnoses and procedures, and established the timing of each diagnosis. APR-DRG Risk of Mortality and Severity of Illness classes were assigned based on (1) all hospital-reported diagnoses, (2) all reabstracted diagnoses, and (3) reabstracted diagnoses present at admission. The outcome variables were 30-day mortality in the 1991-1993 data set and 30-day inpatient mortality in the 1990/1991 validation sample.

Principal findings: The APR-DRG Risk of Mortality class was a strong predictor of death (c = .831-.847), but was further enhanced by adding age and sex. Reabstracting diagnoses improved the apparent performance of APR-DRGs (c = .93 versus c = .87), while using only the diagnoses present at admission decreased apparent performance (c = .74). Reabstracting diagnoses had less effect on hospitals' expected mortality rates (r = .83-.85) than using diagnoses present at admission instead of all reabstracted diagnoses (r = .72-.77). There was fair agreement in classifying hospital performance based on these three sets of diagnostic data (K = 0.35-0.38).

Conclusions: The APR-DRG Risk of Mortality system is a powerful risk-adjustment tool, largely because it includes all relevant diagnoses, regardless of timing. Although some late diagnoses may not be preventable, APR-DRGs appear suitable only if one assumes that none is preventable.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Age Distribution
  • Aged
  • Bias
  • California / epidemiology
  • Comorbidity
  • Diagnosis-Related Groups / classification*
  • Diagnosis-Related Groups / standards*
  • Health Services Research
  • Hospital Mortality / trends
  • Humans
  • Logistic Models
  • Middle Aged
  • Myocardial Infarction / complications
  • Myocardial Infarction / mortality*
  • Outcome Assessment, Health Care / organization & administration
  • Patient Discharge / statistics & numerical data
  • Patient Discharge / trends
  • Predictive Value of Tests
  • Reproducibility of Results
  • Risk Adjustment / methods*
  • Risk Factors
  • Severity of Illness Index*
  • Sex Distribution
  • Single-Blind Method
  • Software Validation