ICD-9-CM coding of emergency department visits for food and insect sting allergy

PURPOSE: Little is known about the role of International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes for identification of specific allergic reactions in the emergency department (ED). METHODS: Investigators in 10 EDs reviewed 1395 charts of consecutive patients presenting with food allergy (ICD-9-CM codes 693.1 and 995.60 to 995.69) and insect sting allergy (code 989.5). They also reviewed charts of patients with "unspecified" allergic reactions (codes 995.0 [other anaphylactic shock] and 995.3 [allergy, unspecified]) to identify additional patients with food or insect sting allergy. RESULTS: Of 406 patients with food allergy, 216 patients (53%) were coded as food allergy, whereas the remaining 190 patients (47%) were not. Of 394 patients with insect sting allergy, 341 (87%) were coded as insect sting allergy, whereas 53 patients (13%) were not. Characteristics of ICD-9-CM-identified compared with chart-review-identified patients differed for both food and insect sting allergy. ICD-9-CM-identified patients with food allergy were less likely to experience anaphylaxis. CONCLUSIONS: Almost half the patients with food allergy would have been missed by using food-specific ICD-9-CM codes alone, whereas only 13% of patients with insect sting allergy would have been missed. Furthermore, characteristics of these allergy patients would have been biased by studying only patients identified by using the allergen-specific ICD-9-CM codes.