New approach for cystic fibrosis diagnosis based on chloride/potassium ratio analyzed in non-invasively obtained skin-wipe sweat samples by capillary electrophoresis with contactless conductometric detection

Abstract

A new approach for sweat analysis used in cystic fibrosis (CF) diagnosis is proposed. It consists of a noninvasive skin-wipe sampling followed by analysis of target ions using capillary electrophoresis with contactless conductometric detection (C4D). The skin-wipe sampling consists of wiping a defined skin area with precleaned cotton swab moistened with 100 μL deionized water. The skin-wipe sample is then extracted for 3 min into 400 μL deionized water, and the extract is analyzed directly. The developed sampling method is cheap, simple, fast, and painless, and can replace the conventional pilocarpine-induced sweat chloride test commonly applied in CF diagnosis. The aqueous extract of the skin-wipe sample content is analyzed simultaneously by capillary electrophoresis with contactless conductometric detection using a double opposite end injection. A 20 mmol/L l-histidine/2-(N-morpholino)ethanesulfonic acid and 2 mmol/L 18-crown-6 at pH 6 electrolyte can separate all the major ions in less than 7 min. Skin-wipe sample extracts from 30 study participants—ten adult patients with CF (25–50 years old), ten pediatric patients with CF (1–15 years old), and ten healthy control individuals (1–18 years old)—were obtained and analyzed. From the analyzed ions in all samples, a significant difference between chloride and potassium concentrations was found in the CF patients and healthy controls. We propose the use of the Cl^-/K⁺ ratio rather than the absolute Cl^- concentration and a cutoff value of 4 in skin-wipe sample extracts as an alternative to the conventional sweat chloride analysis. The proposed Cl^-/K⁺ ion ratio proved to be a more reliable indicator, is independent of the patient's age, and allows better differentiation between non-CF individuals and CF patients having intermediate values on the Cl^- sweat test.

Figure

New approach for cystic fibrosis diagnosis based on skin-wipe sampling of forearm and analysis of ionic content (Cl^-/K⁺ ratio) in skin-wipe extracts by capillary electrophoresis with contactless conductometric detection

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