CFTR and cystic fibrosis: Finally, using the Ussing chamber data in statistical discriminant analyses, together with the clinical outcomes and other laboratory measurements, we report that colonic measurements of CFTR-mediated Cl− secretion, alone or in combination with sweat-Cl− and fecal elastase E1 (FEE), provides the best tool for a discriminative diagnosis among patients with Classic CF, Non-Classic CF and non-CF individuals.