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Comparative Study
. 2014 Sep;13(5):520-7.
doi: 10.1016/j.jcf.2014.05.001. Epub 2014 May 23.

A new method of sweat testing: the CF Quantum®sweat test

Michael J Rock  1 , Linda Makholm  2 , Jens Eickhoff  3
Affiliations
Comparative Study

A new method of sweat testing: the CF Quantum®sweat test

Michael J Rock et al. J Cyst Fibros. 2014 Sep.

Abstract

Background: Conventional methods of sweat testing are time consuming and have many steps that can and do lead to errors. This study compares conventional sweat testing to a new quantitative method, the CF Quantum® (CFQT) sweat test. This study tests the diagnostic accuracy and analytic validity of the CFQT.

Methods: Previously diagnosed CF patients and patients who required a sweat test for clinical indications were invited to have the CFQT test performed. Both conventional sweat testing and the CFQT were performed bilaterally on the same day. Pairs of data from each test are plotted as a correlation graph and Bland-Altman plot. Sensitivity and specificity were calculated as well as the means and coefficient of variation by test and by extremity. After completing the study, subjects or their parents were asked for their preference of the CFQT and conventional sweat testing.

Results: The correlation coefficient between the CFQT and conventional sweat testing was 0.98 (95% confidence interval: 0.97-0.99). The sensitivity and specificity of the CFQT in diagnosing CF was 100% (95% confidence interval: 94-100%) and 96% (95% confidence interval: 89-99%), respectively. In one center in this three center multicenter study, there were higher sweat chloride values in patients with CF and also more tests that were invalid due to discrepant values between the two extremities. The percentage of invalid tests was higher in the CFQT method (16.5%) compared to conventional sweat testing (3.8%) (p < 0.001). In the post-test questionnaire, 88% of subjects/parents preferred the CFQT test.

Conclusions: The CFQT is a fast and simple method of quantitative sweat chloride determination. This technology requires further refinement to improve the analytic accuracy at higher sweat chloride values and to decrease the number of invalid tests.

Keywords: Cystic fibrosis; Newborn screening; Sensitivity; Specificity; Sweat testing.

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Conflict of interest statement

Conflict of Interest Statement

None of the authors have any personal or any financial relationships that would constitute a conflict of interest.

Figures

Figure 1
Figure 1
Electrode and controller set on a child’s arm
Figure 2
Figure 2
CFQT patches: on left, sweat chloride of 16 mmol/L; on right, sweat chloride of 83 mmol/L (as measured by CF analyzer)
Figure 3
Figure 3
CFQT results against conventional sweat test results. Solid line, regression line. Shaded area, intermediate sweat chloride values
Figure 4
Figure 4
Bland-Altman plot of differences between CFQT and conventional sweat chloride versus their average. Solid line, mean difference; dotted lines, mean difference ± 1.96 SD
See this image and copyright information in PMC

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