The Importance of Sweat Testing for Older Siblings of Patients with Cystic Fibrosis Identified by Newborn Screening

We report cystic fibrosis (CF) care center instructions for sweat testing in older siblings after implementation of the French nationwide newborn screening program, and we evaluate the incidence of unrecognized CF. Nearly 9% of families with an infant screened for CF were unaware of an affected older sibling. We strongly recommend sweat testing for all first-degree older children.