Background The Eczema Area and Severity Index (EASI) is an investigator-assessed instrument measuring the severity of clinical signs in atopic dermatitis (AD). The EASI was identified as one of the best-validated outcome measures for AD; however, no previous studies address how to interpret the EASI score for clinical use. Objectives To evaluate the interpretability and the ease of use of the EASI. Methods A retrospective analysis of paediatric and adult patients with AD was performed. Interpretability was evaluated by stratifying the EASI scores according to the Investigator's Global Assessment. The severity strata displaying the highest kappa coefficient of agreement were then selected as the recommended EASI band. The time to administer the EASI was recorded in a subgroup of patients. Results The suggested severity strata for the EASI are as follows: 0 = clear; 0·1-1·0 = almost clear; 1·1-7·0 = mild; 7·1-21·0 = moderate; 21·1-50·0 = severe; 50·1-72·0 = very severe (κ = 0·75). The EASI was also found to be acceptable in terms of ease of use, with assessments by trained investigators taking approximately 6 min. Conclusions Our study provides the first guide for interpreting the EASI score. It enables translation of the EASI numerical output into an AD global severity state that should be more meaningful to providers and patients. Along with a short administration time, the EASI demonstrates adequate feasibility, further supporting its use in clinical trials. What's already known about this topic? The Eczema Area and Severity index (EASI) is one of the best validated outcome instruments for atopic dermatitis (AD). What does this study add? The severity of AD can now be interpreted from the EASI numerical score. The EASI takes a short time to administer. Our study supports the use of EASI as an outcome tool in clinical trials by providing the first guide for interpreting the score and confirming its ease of use.
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