Neonatal screening for cystic fibrosis in São Paulo State, Brazil: a pilot study

ABSTRACT

Cystic fibrosis is one of the most common autosomal recessive hereditary diseases in the Caucasian population, with an incidence of 12000 to 13500 liveborns. More than 1000 mutations have been described with the most common being F508del. It has a prevalence of 23-55 percent within the Brazilian population. The lack of population-based studies evaluating the incidence of cystic fibrosis in São Paulo State, Brazil, and an analysis concerning the costs of implantation of a screening program motivated the present study. A total of 60,000 dried blood samples from Guthrie cards obtained from April 2005 to January 2006 for neonatal screening at 4 reference centers in São Paulo State were analyzed. The immunoreactive trypsinogen (IRT)/IRT protocol was used with the cut-off value being 70 ng/mL. A total of 532 children (0.9 percent) showed IRT >70 ng/mL and a 2nd sample was collected from 418 (80.3 percent) of these patients. Four affected children were detected at two centers, corresponding to an incidence of 18403. The average age at diagnosis was 69 days, and 3 of the children already showed severe symptoms of the disease. The rate of false-positive results was 95.2 percent and the positive predictive value for the test was 8 percent. The cost of detecting an affected subject was approximately US$8,000.00 when this cystic fibrosis program was added to an existing neonatal screening program. The present study clearly shows the difficulties involved in cystic fibrosis screening using the IRT/IRT protocol, particularly in a population with no long-term tradition of neonatal screening.