An evaluation of acuity adjustment metrics to track medication expense over time.

Purpose: The acuity adjustment metric that correlates most closely with actual medication expense at a large, tertiary care academic medical center was investigated.

Methods: This evaluation was conducted at the Ohio State University Wexner Medical Center. All inpatient discharges between July 1, 2012, and March 31, 2013, were included in this study. Patient medical and financial records were used to obtain the diagnosis-related group (DRG) codes and total medication cost for each patient discharge. The primary DRG for each patient was then used to assign the corresponding relative weight (RW) and pharmacy intensity weight (PIW). The correlation between actual and predicted medication expenditure was determined for every DRG for both RW and PIW. Since this compares cost at the DRG level, RW and PIW were used as markers for case-mix index (CMI) and pharmacy intensity score (PIS), respectively.

Results: At this single institution, medication cost per discharge was more strongly correlated with PIW (as a marker for PIS) than with RW (as a marker for CMI). Extrapolating these data to hospital-specific values, the results suggest that PIS is more strongly correlated with overall medication expense than CMI and therefore a better adjustment metric for monitoring medication expense over time.

Conclusion: A single-institution study demonstrated that PIW was more strongly correlated than RW with actual medication expenditure. PIS may be a more accurate acuity metric than CMI for predicting changes in drug expense over time.