To the Editor.—
The report on newborn screening for cystic fibrosis1 illustrates the need for continued evaluation of such programs. The authors state that the identification of cases of cystic fibrosis (CF) by an elevated level of immunoreactive trypsinogen (IRT) in second (follow-up) samples from infants with positive initial screening tests could result in false negatives in 27% of cases of cystic fibrosis without meconium ileus (MI).
We have screened 401 122 infants using the method originally reported.2