Anaphylaxis in a health maintenance organization: International Classification of Diseases coding and epinephrine auto-injector prescribing

Abstract

Background: Accurate estimates of the incidence of anaphylaxis are limited. Current International Classification of Diseases, Ninth Revision (ICD-9) codes complicate accurate diagnosis of anaphylaxis and assessment of appropriate epinephrine prescribing.

Objective: To quantify the incidence and demographic character of patients with anaphylaxis-related ICD-9 codes in a large health maintenance organization and analyze epinephrine prescribing and dispensing rates.

Methods: All patients included had at least 12 months of continuous membership over a 4-year period from January 1, 2008 to December 31, 2012 and were selected based on anaphylaxis-related ICD-9 codes (N = 159,172). This algorithm was extrapolated from a previous study that used expanded ICD-9 codes to identify more cases of anaphylaxis. Individual chart reviews found that many expanded ICD-9 codes represented unconfirmed cases of anaphylaxis and therefore were excluded, resulting in analysis of 52,405 patients.

Results: Incidence of anaphylaxis over 4 years was 2.07%, with female predominance (56.5%) over male predominance (43.5%). Epinephrine was prescribed in 16.2% of total cases. Highest rates of epinephrine prescription were for traditional ICD-9 codes 995.0 (other anaphylactic shock) and 995.60 to 995.69 (anaphylactic shock caused by food) at 49.3% and 58.6%, respectively. Of the cases in which an epinephrine auto-injector was prescribed, it was dispensed 95.9% of the time, independent of copayment amount.

Conclusion: Low epinephrine auto-injector prescribing rates in cases of anaphylaxis suggest the continued difficulty in the diagnosis of anaphylaxis and could result in suboptimal treatment of potential future episodes.