Diagnosis of Cystic Fibrosis Newborn screening May also be suggested by a positive prenatal screening test result, family history, or symptomatic presentation Confirmed by a sweat test showing elevated sweat chloride on 2 occasions Identifying 2 CF-causing variants (1 on each chromosome) is consistent with the diagnosis May rarely be confirmed, in atypical cases, by demonstrating abnormal ion transport across the nasal epithelium or abnormal intestinal current measurements Most cases of CF are first identified by newborn screening, but up to 10% are not diagnosed until adolescence or early adulthood.