title: Utility of ICD-9-CM Codes for Identification of Allergic Drug Reactions.
abstract: BACKGROUND
  The epidemiology of allergic drug reactions is poorly understood due, in large part, to difficulty in identifying true cases in population data sets. Use of International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes is a potentially valuable approach that requires formal evaluation.
  
  
  OBJECTIVE
  To better understand the utility of ICD-9-CM codes for identification of allergic drug reactions, including the validation of specific codes by chart review.
  
  
  METHODS
  We reviewed randomly sampled medical records of patients treated in the emergency department (ED) between January 1, 2001, and December 31, 2006, with ICD-9-CM codes for drug allergy and E codes (E930-949) for adverse drug reactions.
  
  
  RESULTS
  During the 6-year period, 11,130 charts were identified by ICD-9-CM and E codes and 1,634 were reviewed. Allergic drug reactions were found in 444 (27%) of the reviewed ED visits. The codes that identified the highest percentage of true allergic drug reactions were dermatitis due to drug (693.0; 87%), adverse reaction to drug (995.2; 52%), and anaphylaxis (995.0; 38%). Patients with both an ICD-9-CM code and an E code had a high likelihood of having an allergic drug reaction (76%). Most allergic drug reactions were attributed to antibiotics (42%), intravenous contrast (7%), and nonsteroidal anti-inflammatory drugs (6%). The estimated frequency of allergic drug reactions increased from 0.49% of ED visits in 2001 to 0.94% in 2012.
  
  
  CONCLUSIONS
  Specific ICD-9-CM and E codes can be used in combination to identify allergic drug reactions. Further study of these codes in the inpatient and outpatient settings is necessary to better understand the utility of diagnosis codes for improving epidemiologic research on drug allergy.
authors.affiliation: Division of Rheumatology, Allergy, and Immunology, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Mass. Electronic address: rsaff@partners.org.
authors.forename: Rebecca R
authors.initials: RR
authors.lastname: Saff
authors.affiliation: Division of Rheumatology, Allergy, and Immunology, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Mass; Department of Emergency Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Mass.
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Camargo
authors.affiliation: Department of Emergency Medicine, Weill Cornell Medical College, New York, NY.
authors.forename: Sunday
authors.initials: S
authors.lastname: Clark
authors.affiliation: Division of Asthma and Allergy, Department of Pediatrics, Rhode Island Hospital, Alpert School of Medicine at Brown University, Providence, RI.
authors.forename: Susan A
authors.initials: SA
authors.lastname: Rudders
authors.affiliation: Division of Rheumatology, Allergy, and Immunology, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Mass.
authors.forename: Aidan A
authors.initials: AA
authors.lastname: Long
authors.affiliation: Division of Rheumatology, Allergy, and Immunology, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Mass.
authors.forename: Aleena
authors.initials: A
authors.lastname: Banerji
mesh_terms: D000328:Adult; D000485:Allergens / Q000276:immunology*; D000900:Anti-Bacterial Agents / Q000276:immunology*; D004342:Drug Hypersensitivity / Q000175:diagnosis* / Q000453:epidemiology; D004636:Emergency Service, Hospital; D005260:Female; D006801:Humans; D038801:International Classification of Diseases / Q000706:statistics & numerical data*; D008297:Male; D008499:Medical Records; D008875:Middle Aged; D014481:United States; D055815:Young Adult
chemical_list: D000485:Allergens; D000900:Anti-Bacterial Agents
keywords: Adverse drug reactions; Drug allergy; Drug hypersensitivity; Emergency department; Epidemiology; International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes