CFTR and cystic fibrosis: Most US programs use an algorithm that involves at least 1 initial measurement of IRT from a dried blood specimen (DBS) taken from all newborns and then testing for a panel of CFTR mutations on a subset of babies with elevated IRT.7,8 The panel of CFTR mutations can be variable between programs but typically includes the American College of Medical Genetics (ACMG) recommended 23 mutations and often additional mutations.7–10 Newborns with either 1 or 2 CFTR mutations are considered screen positive by most programs and are sent to CF care centers for diagnostic workup.