CFTR and cystic fibrosis: However, the results of our CFTR biomarker measurements at baseline are consistent with previous ICM studies in independent cohorts of patients with CF who are F/F (Bronsveld et al., 2000; Bronsveld et al., 2001; Mall et al., 2004; van Barneveld et al., 2010; Graeber et al., 2018).