Emerging issues in cystic fibrosis newborn screening.

There has been a rise in the introduction of cystic fibrosis (CF) newborn screening (NBS) programs in recent years. Despite many long running and successful programs with established protocols, new strategies are being developed in an effort to improve sensitivity and specificity. In light of the emerging issues of NBS, new algorithms have been implemented and are reviewed here.The increase in mixing of populations affects both immunoreactive trypsinogen values and sensitivity of genetic analysis in NBS. Adjustments to the mutation panel are not always possible. Algorithms adding nongenetic tiers may prove to be an alternative. The interpretation of the sweat test in neonates has been changing too, and there is now agreement that the upper limit of a normal sweat chloride is 29 mmol/l. Infants identified by NBS with a sweat chloride of 30-59 mmol/l and no evidence of two CF-causing mutations require further evaluation and often a long clinical follow-up before CF may be confirmed or excluded. Some NBS programs have reported a steady reduction in the incidence of CF, traceable to prenatal diagnosis on subsequent pregnancies and population-based carrier screening.Although there is not one universal CF NBS protocol that will suit the heterogeneous needs of diverse regions, many options for adjusting algorithms to local conditions are now available.