Changes in fecal elastase-1 following initiation of CFTR modulator therapy in pediatric patients with cystic fibrosis

Background: Improvement in exocrine pancreatic function in persons with CF (pwCF) on cystic fibrosis transmembrane conductance regulator (CFTR) modulators has been documented in clinical trials using fecal pancreatic elastase-1 (FE-1). Our group endeavored to evaluate real-world data on FE-1 in children on CFTR modulator therapy at three pediatric cystic fibrosis (CF) centers.Methods: Pediatric pwCF were offered FE-1 testing if they were on pancreatic enzyme replacement therapy (PERT) and on CFTR modulator therapy according to their center's guideline. FE-1 data were collected retrospectively. The primary outcome was absolute change in FE-1.Results: 70 pwCF were included for analysis. 53 had baseline and post-modulator FE-1 values. There was a significant increase in FE-1 from median 25 mcg/g (IQR 25-60) at baseline to 57 mcg/g (IQR 20-228) post-modulator (p<0.001 by Wilcoxon matched pairs), with an absolute change in FE-1 of median 28 mcg/g (IQR -5-161) and mean 93.5 +/- 146.8 mcg/g. Age was negatively correlated with change in FE-1 (Spearman r=-0.48, p<0.001). 15 pwCF (21%) had post-modulator FE-1 values >= 200 mcg/g, consistent with pancreatic sufficiency (PS). The PS group was significant for younger age at initiation of first CFTR modulator and a higher baseline FE-1.Conclusions: Most pwCF experienced an increase in FE-1 while receiving CFTR modulator treatment and a small percentage demonstrated values reflective of PS. These data suggest that PS may be attained in those that initiated modulator therapy at a younger age or had a higher baseline FE-1. FE-1 testing is suggested for children on any CFTR modulator therapy.