Initial evaluation of a biochemical cystic fibrosis newborn screening by sequential analysis of immunoreactive trypsinogen and pancreatitis-associated protein (IRT/PAP) as a strategy that does not involve DNA testing in a Northern European population.

BACKGROUND: Ethical concerns and disadvantages of newborn screening (NBS) for cystic fibrosis (CF) related to genetic testing have raised controversies and impeded implementation of CF NBS in some countries. In the present study, we used a prospective and sequential immunoreactive trypsinogene (IRT)/pancreatitis-associated protein (PAP) strategy, with IRT as first and PAP as second tier, and validated this biochemical approach against the widely used IRT/DNA protocol in a population-based NBS study in southwest Germany.

METHODS: Prospective quantitation of PAP and genetic analysis for the presence of four mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene most prevalent in southwest Germany (F508del, R553X, G551D, G542X) were performed in all newborns with IRT > 99.0th percentile. NBS was rated positive when either PAP was ≥1.0 ng/mL and/or at least one CFTR mutation was detected. In addition, IRT > 99.9th percentile was also considered a positive rating. Positive rating led to referral to a CF centre for testing of sweat Cl(-) concentration.

FINDINGS: Out of 73,759 newborns tested, 98 (0.13%) were positive with IRT/PAP and 56 (0.08%) with IRT/DNA. After sweat testing of 135 CF NBS-positive infants, 13 were diagnosed with CF. Detection rates were similar for both IRT/PAP and IRT/DNA. One of the 13 diagnosed CF newborns had a PAP concentration <1.0 ng/mL.

CONCLUSIONS: Sequential measurement of IRT/PAP provides good sensitivity and specificity and allows reliable and cost-effective CF NBS which circumvents the necessity of genetic testing with its inherent ethical problems.