CFTR and cystic fibrosis: Measurements of CFTR-mediated Cl– secretion in rectal biopsies of PwCF were previously shown to be the best discriminator of CF diagnosis and prognosis using values of I/F/CCH-stimulated equivalent short-circuit current (I’sc–I/F/C) determined by Ohm’s law from measured transepithelial voltage (Vte) (Mall et al., 2000, 2004; Hug et al., 2011; Sousa et al., 2012).