Rate and predictors of insufficient sweat volume in very young infants after pilocarpine gel iontophoresis: prospective, population-based study.

Objective: To verify the rate and predictors of 'quantity not sufficient' (QNS) among Brazilian infants younger than 3 months with positive newborn screening (NBS) for cystic fibrosis (CF).

Methods: Prospective, population-based study. Methods: Public Statewide Newborn Screening Programme where the incidence rate of CF is ≈1:11 000. Methods: Subjects with positive two-tiered immunoreactive trypsinogen. Methods: Sweat induction and collection were performed in the same facility; one sweat sample was obtained per individual. Methods: The QNS rate and its predictors; analysis corresponded to the day of sweat collection.

Results: Among the 975 participants, QNS rates for 10 and 15 µL were 3.6% (95% CI 2.5% to 4.9%) and 8.3% (95% CI 6.6% to 10.2%). Infants weighing >3056 and >3845 g and with gestational age higher than 37 weeks had a greater likelihood (5.5 and 6.7, and 2.7 and 5.8 times more, respectively) of avoiding QNS than their peers.

Conclusions: QNS rates fulfilled the requirements, but predictors differed from those recommended by the Cystic Fibrosis Foundations guidelines.