Development and Validation of a Disease Severity Index for Patients With Cold Urticaria

BACKGROUND: Cold urticaria (ColdU) is a common type of chronic inducible urticaria where cold induces wheals and/or angioedema, with a wide range of disease severity, from very mild to life-changing and life-threatening, based on symptoms, day-to-day burden, general response to therapies, the need for cold avoidance, and the use of emergency treatment. There are no validated instruments to objectively assess disease severity in patients with ColdU.

OBJECTIVE: To develop and validate a disease-specific Severity Index for ColdU (SICU).

METHODS: The development of the SICU followed 4 phases: (1) conceptual framework, (2) item generation, (3) item reduction, and (4) final editing. Seven and eight patients were interviewed in the item generation phase and in the item reduction phase, respectively. Then, a validation study with 75 patients was performed, which included construct, structural, convergent, and known-group validity assessments as well as the characterization of reliability (internal consistency and test-retest).

RESULTS: The preliminary tool consisted of 24 items. After item reduction, the final SICU included 13 items and 4 domains: "trigger factors," "signs and symptoms," "quality of life," and "therapy and efficiency." The validation study revealed appropriate structural and construct validity with excellent measures of sample adequacy, appropriate convergent validity, as well as an adequate known-group validity, high internal consistency, and high test-retest reliability.

CONCLUSIONS: The SICU is the first validated disease-specific patient-reported outcome measure (PROM) for assessing ColdU disease severity. This PROM will facilitate patient care by evaluating disease severity and consequently better informing physicians and patients on an appropriate therapeutic approach.