We read with interest the review of the American Society of Anesthesiologists (ASA; Schaumburg, Illinois) Physical Status Classification System by Horvath et al. The authors provided an overview of the ASA Physical Status system; however, one use of the ASA Physical Status system is not mentioned that we believe warrants attention due to its impact on hospital finances and quality ratings.
The ASA Physical Status score is a key variable in mathematical models used by the Centers for Disease Control and Prevention (Atlanta, Georgia) National Healthcare Safety Network to risk-adjust surgical site infection rates at U.S. acute care hospitals. For each hospital, a standardized infection ratio is calculated for colon surgery and abdominal hysterectomy. The standardized infection ratio is calculated by dividing the observed number of infections for each procedure by the expected number of infections. A standardized infection ratio greater than 1 indicates better than expected performance, whereas a standardized infection ratio less than 1 indicates worse than expected performance. The probability of infection for each patient is calculated using logistic regression equations that incorporate patient, procedural, and facility factors that have been found to predict surgical site infection incidence (table 1). The total number of expected infections is equal to the sum of the probabilities for all patients over a given period.2 The ASA Physical Status score is the only variable that is subjective and therefore prone to misclassification. Systematic underreporting of ASA Physical Status will adversely impact a hospital’s risk-adjusted surgical site infection performance, whereas overreporting (up-coding) will artificially improve a hospital’s performance.