Comparison of quantitative sweat chloride methods after positive newborn screen for cystic fibrosis.
OBJECTIVE
Rapid and reliable confirmatory sweat testing following a positive newborn screen (NBS) for cystic fibrosis (CF) is preferred to allow for early diagnosis and to decrease parental anxiety. The Cystic Fibrosis Foundation (CFF) recently recommended a quantity not sufficient (QNS) rate of ≤ 10% in infants <3 months of age referred for quantitative sweat chloride analysis. Two CFF-approved methods are available by which to quantitatively measure chloride concentration in sweat. Our objective was to compare the performance of the Macroduct® sweat collection system (MSCS) with the Gibson and Cooke technique (GCT) in the acquisition of samples for the determination of sweat chloride concentration in infants with a positive Minnesota State NBS for CF.


METHODS
A retrospective database review of infants referred to the core Minnesota CF Center or its affiliate site for confirmatory sweat testing was performed to compare the QNS rates for the two techniques. Associations between birthweight, age at test, race, and QNS rates were examined.


RESULTS
Five hundred sixty-eight infants were referred for 616 sweat tests from March 2006 to January 2010. The mean age was 32.8 days at the initial sweat test. The GCT had a significantly higher QNS rate compared to the MSCS (15.4% vs. 2.1%, P < 0.0001). There was no association between age and the probability of QNS. The probability of QNS decreased as birthweight increased (P = 0.02). After adjusting for age, the odds of QNS using the GCT remained 8.34 (95% CI: 3.72-18.71) times that of the MSCS. Non-White infants had a significantly higher likelihood of QNS compared to non-Hispanic White infants (P = 0.0025).


CONCLUSIONS
Given the performance of the MSCS, the Minnesota CF Center has implemented the MSCS as its method of choice for diagnostic sweat testing in infants following a positive state NBS.
Department of Pediatrics, University of Minnesota School of Medicine and The Amplatz Children's Hospital, Minneapolis, Minnesota, USA. lagun005@umn.edu
Theresa A
TA
Laguna
Nan
N
Lin
Qi
Q
Wang
Bonnie
B
Holme
John
J
McNamara
Warren E
WE
Regelmann
D002712:Chlorides / Q000032:analysis*; D003550:Cystic Fibrosis / Q000175:diagnosis*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007478:Iontophoresis / Q000379:methods*; D008297:Male; D018721:Muscarinic Agonists; D015997:Neonatal Screening / Q000379:methods; D010862:Pilocarpine; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013542:Sweat / Q000737:chemistry*
D002712:Chlorides; D018721:Muscarinic Agonists; D010862:Pilocarpine