CFTR and cystic fibrosis: Patients are diagnosed with this condition if they possess a positive newborn screen for CF and either of the following criteria: (1) normal sweat chloride value (<30 mEq/L) and two identified CFTR variants, at least one of which exhibits unclear phenotypic consequences; or (2) intermediate sweat chloride value (30–59 mEq/L) and detection of one or zero CF-causing variants [16].