Development and validation of a US quality of life instrument for hereditary angioedema due to C1 inhibitor deficiency

Background: Hereditary angioedema (HAE) attacks are unpredictable, cause a substantial and enduring burden of illness, and are potentially fatal. Because of issues unique to the US health care system, there is a need for a US-validated, HAE-specific quality of life (QoL) instrument. Objective: To develop and validate a US HAE-specific QoL instrument according to US Food and Drug Administration guidelines and established methodologies. Methods: We generated 41 QoL-related items likely relevant to US patients with HAE due to C1 inhibitor (C1INH) deficiency (HAE-C1INH) and performed a 10-patient pilot study to refine the question wording. A total of 415 US patients with HAE-C1INH completed the initial 41-item instrument online, thereby providing data for item reduction, factor analysis, and the assessment of validity and reliability. We used a multiple linear regression to identify the drivers of the total and domain scores. Convergent validity analysis was used to assess the extent to which the HAE-C1INH QoL instrument (HAE-C1INH-QoL) is theoretically related to the angioedema-QoL instrument (AE-QoL). Results: Item reduction and factor analysis yielded a final instrument of 31 items across 5 domains, and the assessment analysis showed that the HAE-C1INH-QoL is valid and reliable. Attack frequency and severity were statistically significant factors that influenced the total and domain scores. Correlation analysis of the 2 instruments indicated that 8 items of the HAE-C1INH-QoL were not included or well-described in the AE-QoL. Conclusion: The HAE-C1INH-QoL is the first HAE-specific QoL tool validated in the United States. When compared with the AE-QoL, the items in our instrument are more relevant to US patients with HAE.