Can pharmacy data improve prediction of hospital outcomes? Comparisons with a diagnosis-based comorbidity measure.

OBJECTIVES: The performance of comorbidity measures derived from the hospital discharge abstract, the outpatient pharmacy record, and from both sources combined, were compared in predicting all-cause and unplanned hospital readmission and length of stay.
MATERIALS AND METHODS: Automated hospital and pharmacy data came from Kaiser-Permanente and included 6721 acute hospitalizations in Southern California from April 1993 to February 1995. The Deyo adaptation of Charlson's 17 comorbidities was derived from hospital discharge data and the 29 Chronic Disease Score (CDS) comorbidity markers were derived from outpatient pharmacy claims data. Logistic and OLS regression models were used to compare the performance of each measure in baseline models and to evaluate whether the CDS contributed additional explanatory power in a combined model.
RESULTS: The CDS was a significant predictor of unplanned readmission (C = 0.68) and LOS (Adjusted R(2) = 0.26) in multivariable models adjusted for baseline patient demographic and hospitalization characteristics. The Deyo measure was a significant predictor of all-cause readmission (C = 0.63), unplanned readmission (C = 0.68), and LOS (Adjusted R(2) = 0.26). When pharmacy-based disease markers were added to the Deyo baseline model, modest, statistically significant improvements in predictive power were noted in the unplanned readmission and LOS models.
CONCLUSIONS: The finding that both measures of comorbid disease demonstrated similar predictive power is noteworthy, because secondary diagnosis data document relevant illness in hospital patients and pharmacy claims data were never intended for that purpose. The results suggest that small improvements in model performance may come from combining both sources of data in models to predict hospital readmission and LOS.