Comparison between two newborn screening strategies for cystic fibrosis
in Argentina: IRT/IRT vs. IRT/PAP
Abstract
Background: Benefits of early Cystic Fibrosis (CF) detection using
newborn screening (NBS) lead to widespread use in NBS programs. Since
2002, a two-stage immunoreactive trypsinogen (IRT/IRT) screening
strategy has been used as CFNBS method in all public maternities in the
City of Buenos Aires, Argentina. However, novel screening strategies may
be more efficient. The aim of the study is to prospectively compare two
CFNBS strategies, IRT/IRT and IRT/PAP (pancreatitis-associated protein).
Methods: A two-year prospective study was performed. IRT was measured in
dried blood samples collected 48–72 hours after birth. When IRT value
was abnormal, PAP was determined, and a second visit was scheduled to
obtain another sample for IRT before 25 days of life. Newborns with a
positive CFNBS were referred for confirmatory sweat test. Results: There
were 69,827 births in the City of Buenos Aires during the period
studied; 918 (1.31%) had an abnormal IRT. A total of 207 children
(22.5%) failed to return for the second IRT, but only two PAP (0.2%)
were not performed. IRT/IRT was more likely to lead to a referral for
sweat testing than IRT/PAP (OR 2.3 [95% CI 1.8;2.9],
p<0.001). Sensitivity, specificity, positive predictive value,
and negative predictive value were: 80% and 100%, 86.5% and 82.6%,
4.04% and 4.2%, 99.84% and 100% for IRT/IRT and IRT/PAP strategies,
respectively. Conclusion: The IRT/PAP strategy is more sensitive than
IRT/IRT; it avoids a second appointment and the need of unnecessary
sweat testing, and decreases loss to follow up in our population.