Development and Initial Validation of a Questionnaire to Measure Health-Related Quality of Life of Adults with Common Variable Immune Deficiency: The CVID_QoL Questionnaire.

BACKGROUND: Generic health status quality of life (QoL) instruments have been used in patients with common variable immune deficiency (CVID). However, by their nature, these tools may over- or underestimate the impact of diseases on an individual's QoL. OBJECTIVE: The objective of this study was to develop and validate a questionnaire to measure specific-health-related QoL for adults with CVID (CVID_QoL). METHODS: The 32-item content of the CVID_QoL questionnaire was developed using focus groups and individual patient interviews. Validation studies included 118 adults with CVID who completed Short Form-36, Saint George Respiratory Questionnaire, General Health Questionnaire-12, and EuroQol-5D questionnaire in a single session. Principal component and factor analysis solutions identified 3 scores to be similar in number and content for each solution. Validation of 3 factor scores was performed by construct validity. Reproducibility, reliability, convergent validity, and discriminant validity were evaluated. Matrices consisting of correlations between the 32 items in the CVID_QOL were calculated. RESULTS: Factor analysis identified 3 dimensions: emotional functioning (EF), relational functioning (RF), and gastrointestinal and skin symptoms (GSS). The instrument had good internal consistency (Cronbach's alpha, min. 0.74 for GSS, max. 0.84 for RF, n = 118) and high reproducibility (intraclass correlation coefficient, min. 0.79 for RF, max 0.90 for EF, n = 27). EF and RF scores showed good convergent validity correlating with conceptually similar dimensions of other study scales. Acute and relapsing infections had a significant impact on EF and RF. CONCLUSIONS: This study provides evidence of the reliability and construct validity of the CVID_QoL to identify QoL issues in patients with CVID that may not be addressed by generic instruments.