Sweat chloride quantification using capillary electrophoresis

Abstract

Background: Cystic fibrosis (CF) is the less rare and severe genetic disease among the European population. Biochemical diagnosis of CF is based on the demonstration of increased chloride concentration in sweat samples, obtained during the sweat test (ST). WynSep developed a capillary electrophoresis with contactless conductivity detection (CE-C4D) able to measure sweat chloride with a low sample volume. We evaluated the clinical feasibility of this device in a cohort of patients suspected of CF, in comparison with the common coulometric method (ChloroChek chloridometer).

Methods: We determined sweat chloride concentration of 65 samples from patients referred to our institution to undergo a sweat test. Each sample was submitted to coulometric method first, then WynSep-CE, with or without internal standard (IS) subject to sufficient volume sample.

Results: A total of 53 samples were analysed by both coulometric and WynSep-CE (using IS) methods. The method validation showed comparable analytical performances for both methods; no false positive or false negative was recorded. The two methods showed a high correlation (r = 0.993, p < 0.001) and a close agreement was demonstrated by two different statistical tests (Bland-Altman and Passing-Bablok).

Conclusions: WynSep-CE is an accurate, fast, easy-to-use and an appropriate method for CF diagnosis.

Keywords: CE, capillary electrophoresis; CF, cystic fibrosis; CFTR, cystic fibrosis transmembrane conductance regulator; CV, coefficient of variation; Capillary electrophoresis; Chloride; Cystic fibrosis; IS, internal standard; LOD, limit of detection; ST, sweat test; Sweat test.

Fig. 1

Electropherograms of chloride analysis for CF diagnosis. A: Standard solution; B: Control (non-CF) patient and C: CF pathologic samples. Separations carried out on a Wyn-CE system (WynSep). CE conditions were as follows: neutral coated 50 µm DI capillary 35-cm total length and 23-cm effective cathodic length; background electrolyte (BGE): CF-Buffer from WynSep; voltage − 25 kV; C4D detection; hydrodynamic injection under 50 mbars during 5 s. Chloride concentrations: 96 mmol/L for pathologic sample, 13 mmol/L for Healthy sample, and 43 mmol/L for standard solution. Internal Standard: sulfate at 100 µM.

Fig. 2

Comparison between data obtained by CE and reference coulometric method by Bland-Altmann test (A: the central line show the mean differences between methods, upper and lower lines correspond to± 1.96 times the standard deviation) and Passing-Bablok regression (B: the dotted lines indicate the envelope of± 95% confidence limits about the regression, shown in a thick black line). CI, confidence interval. Concentrations are expressed in mmol/L.