Validation of the Dermatology Life Quality Index as an outcome measure for urticaria-related quality of life

Background: Chronic idiopathic urticaria (CIU) is a debilitating skin disease that affects patients' quality of life (QOL). The Dermatology Life Quality Index (DLQI) assesses QOL parameters across several types of dermatologic conditions. However, an evaluation of the validity of the DLQI for use in CIU patients has not been undertaken, because CIU, unlike other chronic skin conditions, is subject to daily or weekly symptom fluctuations. Objective: To test the reliability and validity of the DLQI in 2 samples of CIU patients treated with fexofenadine hydrochloride (20, 60, 120, or 240 mg twice daily). Methods: Data were obtained from 2 similar multicenter, double-blind, randomized, placebo-controlled, parallel-group studies of CIU patients (n = 418 and n = 439). Patients completed the 10-item DLQI during 3 clinic visits (approximately 2 weeks apart). Clinic personnel also recorded patients' symptoms. Results: The results of the DLQI items were similar to those obtained with other skin disease populations, indicating the presence of relatively symmetrical distributions. Reliability was high, demonstrating the lack of excessive random measurement error (a coefficient = .89 and .87 for samples 1 and 2). Factor analysis resulted in a unidimensional pattern, supporting the use of a total DLQI score. Most DLQI items distinguished patients with varying degrees of QOL impairment, highlighting the sensitivity of this instrument. Construct validity was moderate, providing evidence that the DLQI was responsive to changes in patients' clinical status. Conclusions: The DLQI is a valid, reliable, and clinically useful outcome measure for assessing QOL in CIU patients.