- Cade A, Walters M, McGinley N, Firth J, Brownlee K, Conway S, et al. Evaluation of fecal pancreatic elastase-1 as a measure of pancreatic exocrine function in children with cystic fibrosis. Pediatr Pulmonol. 2000;29:172-6 pubmed..The low values in the first 2 weeks in some normal and premature infants, and the persisting normal values in PS infants, make the fecal EL-1 test unsuitable for neonatal CF screening. ..