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Published on: September 13, 2018
Quantity not sufficient rates and delays in sweat testing in US infants with cystic fibrosis
Susanna A McColley1,2, Alexander Elbert3, Runyu Wu3
1Department of Pediatrics, Northwestern University Feinberg School of Medicine, Chicago, Illinois.
Insights
Infants with positive cystic fibrosis (CF) newborn screening tests often have insufficient sweat volumes for testing. However, most infants under two weeks old provide adequate samples, so sweat testing should not be delayed.
Area of Science:
- Pediatrics
- Genetics
- Medical Diagnostics
Background:
- Diagnostic sweat testing is crucial for infants with positive newborn screening (NBS) for cystic fibrosis (CF).
- Infants frequently yield "quantity not sufficient" (QNS) sweat volumes, more so than older children.
- A detailed study on QNS sweat volumes specifically in infants was previously lacking.
Purpose of the Study:
- To comprehensively analyze QNS sweat volumes in infants undergoing sweat testing.
- To determine QNS rates in infants based on age, particularly in the first 60 days of life.
- To compare QNS rates between preterm and term infants.
Main Methods:
- Surveyed US Cystic Fibrosis (CF) Centers for QNS rates in infants tested before 14 days and 3 months of age.
- Analyzed Cystic Fibrosis Foundation Patient Registry (CFFPR) data from 2010-2018 for QNS rates in 10-day increments up to 60 days.
- Compared QNS rates in preterm (<37 weeks gestational age) versus term infants and assessed age at testing.
Main Results:
- 27% of surveyed CF Centers reported a mean QNS rate of 10.5% in infants 14 days or younger.
- CFFPR data indicated higher QNS rates in the youngest infants and those born preterm.
- Over 22% of infants lacked a reported sweat test by 60 days, despite a decreasing median age at testing.
Conclusions:
- While younger infants with CF show higher QNS rates, over 80% of those under two weeks yield sufficient sweat volumes.
- Sweat testing for cystic fibrosis should proceed promptly in infants with positive NBS results.
- Early sweat testing is feasible and recommended for infants identified through newborn screening.
Background:
Diagnostic sweat testing is required for infants with positive newborn-screening (NBS) tests for cystic fibrosis (CF). Infants have "quantity not sufficient" (QNS) sweat volumes more often than older children. A comprehensive study of QNS sweat volumes in infants has not previously been reported.
Methods:
We surveyed US CF Centers to obtain QNS rates in all infants who had sweat testing at under 14 days and under 3 months of age. We then calculated QNS rates reported to the Cystic Fibrosis Foundation Patient Registry (CFFPR) 2010-2018 in 10-day increments from 1 to 60 days of life. We compared QNS sweat test rates in preterm (<37-weeks gestational age) vs term infants. We assessed age at sweat test and proportion of infants who did not have a sweat test reported by 60 days of age.
Results:
Thirty-nine of 144 (27%) of CF Centers reported a mean QNS rate of 10.5% (range, 0-100) in infants 14-days-old or younger. CFFPR data showed the highest QNS rates in the youngest infants and in those born before 37 weeks of gestation. The median age at sweat testing decreased over time, but more than 22% of infants did not have a sweat test reported by 60 days.
Conclusion:
Higher QNS rates are seen in the youngest infants with CF, but more than 80% of infants younger than 2 weeks of age have adequate sweat volumes. Sweat testing should not be delayed in infants with a positive CF NBS test.
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