Interviews were conducted by telephone between June 2018 and September 2018 by one of three interviewers from ICON plc, a global contract research organization. Each interviewer received project-specific training in qualitative interviewing and in maintaining patient confidentiality. The interviews were conducted following a non-scripted, semi-structured interview guide with open-ended questions to collect spontaneously reported information. If the patient being interviewed did not cover specific topics of interest, then the interviewer probed these topics as instructed in the interview guide. The interview guide (Additional file 1: Table S1) included topics that corresponded to the concepts covered by items in the AE-QoL. Covering the AE-QoL items in the guide enabled a comparison of concepts elicited during the interviews and those in the AE-QoL via a conceptual mapping correspondence analysis. The interview guide also included topics that AE-QoL items did not address to determine whether the AE-QoL sufficiently addressed concepts of interest to patients treated with C1INH(SC).

Each 1-h interview took place at a time agreed upon by each patient prior to the interview. At the completion of the interview, each patient received compensation of 100 USD in the form of a gift card for their participation. The interviews were audio recorded with the patients’ permission, transcribed verbatim by a third-party vendor, and anonymized to remove all personally identifiable information. Audio recordings were destroyed after analysis of the interviews was completed.