Presentation (CTI)

OBJECTIVES: Adverse events (AEs) involving inpatient cases are an important consideration in economic evaluations. Variation in estimates by data source can impact the accuracy of cost estimates. In Canada, AE costs are typically based on publicly-available mean costs estimated at the case-mix group (CMG) level. This study aimed to assess the accuracy of AE costing using CMG mean costs vs. more granular ICD-10-CA-based costs.
METHODS: Mean and median costs of commonly-reported AEs (n=100) by mapped ICD-10-CA codes with the most responsible diagnosis were provided by the Canadian Institute for Health Information (CIHI). These AEs were then mapped to CMG groupings to facilitate comparison. Differences between the mean and median ICD-10-CA and CMG costs; and mean and median ICD-10-CA costs, were estimated.
RESULTS: The difference in ICD-10-CA costs relative to best-matched CMGs ranged from -$5,188 to $35,956 (-44% to 344%), with 42% of AEs having an absolute percentage difference of >50%. The average absolute difference in costs was $5,343 (68%). The majority (76%) of AEs had a higher mean ICD-10-CA than CMG cost. The AEs with the largest absolute difference in mean costs were immune system disorders ($11,690; 117%) and infections/infestations ($9,549; 116%). The difference in median ICD-10-CA costs relative to the mean ranged from -81% to 17%, with lower median costs for 95% of AEs. The average absolute difference between median and mean ICD-10-CA costs was $5,271.
CONCLUSIONS: Publicly-available CMG costs are an imprecise proxy for inpatient AE costs, likely underestimating the true hospital costs associated with managing AEs. Mean costs likely overestimate typical AE costs due to high-cost outliers, evidenced by means consistently exceeding medians; median costs may be more precise but are currently not made publicly available. Costing AEs based on ICD-10-CA level data provides a more accurate reflection of the economic impact of AEs.