Rate and predictors of quantity not sufficient of sweat for chloridrometry in very young infants

The Cystic Fibrosis Foundation (CFF) defines a quantity not sufficient (QNS) of sweat as a sample weighting lower than 75 mg, whose rate should be lower than 10% for infants younger than three months. This study aimed to verify the rate and factors associated with QNS for chloridrometry among very young babies from a low-prevalence resource-limited setting.
We recruited prospectively and consecutively newborns and young infants younger than three months undergoing coulometry assays after two abnormal immunoreactive trypsinogen results. Explanatory variables were gender, gestational age (<37 or >37 weeks), birth weight (<2.500 g or >2.500 g), weight on the day of sweat collection (<2.500 g or >2.500 g), age upon the sweat test (<43 or >43 days), daily weight gain from birth to the day of sweat collection (<25 or >25 g/day). Statistical included frequency distribution and univariate and multivariate logistic regression analyses.
One thousand sixteen individuals were included. Mean and median ages were 48 days (SD 19.4) and 43 days (range 15-90 days), respectively, and 50.7% were girls. The rate of QNS was 3.3%. Preterm (OR = 3.7), with weight on the day of sweat collection under 2.500 g (OR = 7.1) and lower daily weight gain (OR = 10.1), were more likely to produce insufficient sweat amounts.
QNS rate for chloridrometry fulfilled CFF standards in the studied population. Ideally, in the case of QNS, sweat testing should be postponed as early as possible when the infant attains more than 37 weeks (corrected age), 2.500 g on the day of sweat collection, and an optimal daily weight gain.

What is already known about this topic? Insufficient amount of sweat should be lower than 5% and 10% in infants older and younger than three months undergone sweat testing; weight lower than 2000-3000 g, and prematurity are predictors of insufficient sweat samples. What does this article add to our knowledge? Collection of a sufficient amount of sweat is feasible in resource-limited settings; daily weight gain from birth to the date of sweat collection is an additional non-negligible predictor for a lower amount of sweat. How does this study impact current management guidelines? In resource-limited settings, QNS rates could fulfill international standards among infants by postponing sweat testing when they attain 37 weeks of gestational age, weight gain of 25 g/day, and 2500 g on the day of sweat collection.

: May 29, 2023
Accepted: July 6, 2023
Published: Sept 1, 2023

Table of Contents: Vol. 1, n. 3, September 2023

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