CFTR and cystic fibrosis: The diagnosis can be made through the identification of two mutations in the CF gene, two abnormal results of the sweat test, or the presence of at least one of the following symptoms: obstructive/suppurative lung disease or chronic sinus disease, chronic exocrine pancreatic failure or family history of CF.2, 4 For patients in whom the chloride concentration in sweat is normal or borderline and in which mutations in the two CF genes are not identified, the nasal potential difference (NPD) measurement can be used as evidence of CFTR dysfunction.