The combination of elexacaftor/tezacaftor/ivacaftor (ETI) is effective in people with cystic fibrosis (CF) with at least one F508del-CFTR allele; however, approximately 10% have variants without established ETI responsiveness and are ineligible for therapy. Additionally, diagnostic confirmation or exclusion of CF can be challenging in individuals with compatible symptoms, CFTR variants of unknown significance, and indeterminate sweat chloride or nasal potential difference (NPD) results. We...