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Comparative Study
. 2012 Aug;47(8):736-42.
doi: 10.1002/ppul.21608. Epub 2012 Jan 3.

Comparison of quantitative sweat chloride methods after positive newborn screen for cystic fibrosis

Theresa A Laguna  1 , Nan Lin, Qi Wang, Bonnie Holme, John McNamara, Warren E Regelmann
Affiliations
Comparative Study

Comparison of quantitative sweat chloride methods after positive newborn screen for cystic fibrosis

Theresa A Laguna et al. Pediatr Pulmonol. 2012 Aug.

Abstract

Objectives: 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.

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Figures

Figure 1
Figure 1
QNS rates vs. Age at Initial Test for all infants presenting to the University of Minnesota CF Center and Children’s Hospitals and Clinics of Minnesota for a sweat test following a positive CF NBS. The association between QNS for the GCT (Panel A)/MCS (Panel B) and age at initial test was not significant (p = 1.0 and p = 0.28, respectively). Error bars represent 95% confidence intervals (CI).
Figure 2
Figure 2
QNS rates vs. Birthweight for all infants presenting to the University of Minnesota CF Center and Children’s Hospitals and Clinics of Minnesota for a sweat test following a positive CF NBS. The probability of QNS decreases significantly as birthweight increases in both the GCT (p = 0.023) and MCS methods (p = 0.022). Error bars represent 95% CI.
Figure 3
Figure 3
QNS rates vs. Weight at Test for infants presenting to the University of Minnesota CF Center for a sweat test (GCT) following a positive CF NBS. The probability of a QNS decreases significantly as weight at time of test increases (p< 0.001). Error bars represent 95% CI.
See this image and copyright information in PMC

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