Impact of an Antimicrobial Allergy Label in the Medical Record on Clinical Outcomes in Hospitalized Patients

STUDY OBJECTIVE: To determine the impact of having an antimicrobial allergy label in the medical record on clinical outcomes in hospitalized patients. DESIGN: Retrospective cohort study. SETTING: Urban academic teaching hospital. PATIENTS: A total of 11,872 adults admitted to nonsurgical patient care wards who received at least one antimicrobial between August 1, 2007, and July 31, 2008; of these patients, 1324 (11.2%) had an antimicrobial allergy label and 10,548 (88.8%) did not have an allergy label documented in the medical record. MEASUREMENTS AND MAIN RESULTS: The following clinical outcomes were compared in patients with allergy labels versus patients without allergy labels: length of stay, admission to the intensive care unit (ICU), number of antimicrobials received during hospitalization, readmission within 4 weeks of hospital discharge, and death during hospitalization. Presence of an allergy label in the medical record was associated with increased length of stay, a higher ICU admission rate, receipt of more than one antimicrobial, and a higher mortality rate during the hospitalization. Logistic regression models were used to assess the association of allergy label with these outcomes while adjusting for covariates (age group, sex, surgery during hospitalization, and season of admission); multiple regression was used to model the association of allergy label with length of stay. On average, length of stay was 1.21 days (unadjusted) and 1.16 days (adjusted for covariates) longer in patients with allergy labels. The likelihood of an ICU admission were 1.4 times (adjusted odds ratio OR 1.42, 95% confidence interval CI 1.21-1.67) higher in patients with allergy labels. Presence of an allergy label was also associated with receipt of more than one antibiotic during the hospitalization (crude OR 1.61, 95% CI 1.43-1.81) and a 1.6-fold higher risk of dying during the hospitalization (crude OR 1.56, 95% CI 1.20-2.04). Presence of an allergy label was not associated with an increased risk of readmission within 4 weeks of discharge (adjusted OR 0.71, 95% CI 0.63-0.80). CONCLUSION: Presence of an allergy label in the medical record was associated with increased length of hospital stay and worse clinical outcomes compared with no allergy label in hospitalized patients treated with antimicrobials.