Research Article| Volume 22, ISSUE 1, P66-72, January 2023

Rapid chloride and bicarbonate determination by capillary electrophoresis for confirmatory testing of cystic fibrosis infants with volume-limited sweat specimens


      • An assay for sweat chloride and bicarbonate determination was developed by capillary electrophoresis.
      • Good mutual agreement for sweat chloride was achieved as compared to coulometric titration for CF confirmatory testing.
      • Sweat bicarbonate did not have clinical diagnostic value to differentiate CF infants from unaffected carriers.
      • This method may reduce testing failure rates caused by insufficient sweat volume collected from infants.


      Objectives Cystic fibrosis (CF) is a debilitating genetic disorder that benefits from early detection. CF diagnosis relies on measuring elevated sweat chloride that is difficult in neonates with low sweat rates. We introduce a new method for sweat chloride determination from volume-limited specimens, and explore the potential utility of sweat bicarbonate in neonatal CF screening.
      Methods A rapid assay (< 5 min) was developed to analyze chloride and bicarbonate using capillary electrophoresis with indirect UV detection (CE-iUV). Pilocarpine-stimulated sweat samples from screen-positive CF infants were collected at two hospital sites, including confirmed CF (n = 12), CF screen-positive inconclusive diagnosis (n = 4), and unaffected non-CF cases (n = 37). All sweat chloride samples were analyzed by a coulometric titrator and CE-iUV, and the viability to measure acid-labile bicarbonate was also evaluated.
      Results Stability studies revealed that bicarbonate can be reliably assessed in sweat if acidification and heating were avoided. Method validation demonstrated that sweat chloride and bicarbonate were quantified with acceptable accuracy (recovery of 102%), precision (CV = 3.7%) and detection limits (∼ 0.1 mM). An inter-laboratory comparison confirmed a mean bias of 6.5% (n = 53) for sweat chloride determination by CE-iUV relative to a commercial chloridometer. However, sweat bicarbonate did not discriminate between CF and non-CF infants (AUC = 0.623, p = 0.215) unlike chloride (AUC = 1.00, p = 3.00 × 10−7).
      Conclusions CE-iUV offers a robust method for sweat chloride testing from presumptive CF infants that may reduce testing failure rates. However, sweat bicarbonate does not have clinical value in newborn CF diagnosis.


      To read this article in full you will need to make a payment

      Purchase one-time access:

      Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
      One-time access price info
      • For academic or personal research use, select 'Academic and Personal'
      • For corporate R&D use, select 'Corporate R&D Professionals'


      Subscribe to Journal of Cystic Fibrosis
      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect


        • Goetz D.
        • Ren C.L.
        Review of cystic fibrosis.
        Pediatr Ann. 2019; 48: e154-e161
        • Mak D.Y.F.
        • Sykes J.
        • Stephenson A.L.
        • Lands L.C.
        The benefits of newborn screening for cystic fibrosis: the Canadian experience.
        J Cystic Fibrosis. 2016; 15: 302-308
        • Rosenfeld M.
        • Sontag M.K.
        • Ren C.L.
        Cystic fibrosis diagnosis and newborn screening.
        Pediatr Clin N Am. 2016; 63: 599-615
        • Baker M.
        • Atkins A.
        • Cordovado S.
        • et al.
        Improving newborn screening for cystic fibrosis using next-generation sequencing technology: a technical feasibility study.
        Genet Med. 2016; 18: 231-238
        • Quinton P.M.
        Chloride impermeability in cystic fibrosis.
        Nature. 1983; 301: 421-422
        • Collie J.T.B.
        • Massie R.J.
        • Jones O.A.H.
        • et al.
        Sixty-five years since the New York heat wave: advances in sweat testing for cystic fibrosis.
        Pediat Pulmonol. 2014; 49: 106-117
        • Simmonds N.J.
        Is it cystic fibrosis? The challenges of diagnosing cystic fibrosis.
        Paediatr Respir Rev. 2019; 31: 6-8
        • Gonska T.
        • Keenan K.
        • Au J.
        • et al.
        Outcomes of cystic fibrosis screening-positive infants with inconclusive diagnosis at school age.
        Pediatrics. 2021; 148e2021051740
        • Servidoni M.F.
        • Gomez C.C.S.
        • Marson F.A.L.
        • et al.
        Sweat test and cystic fibrosis: overview of test performance at public and private centers in the state of São Paulo, Brazil.
        J Bras Pneumol. 2017; 43: 121-128
        • Gokdemir Y.
        • Vatansever P.
        • Karadag B.
        • et al.
        Performance evaluation of a new coulometric endpoint method in sweat testing and its comparison with classic Gibson&Cooke and chloridometer methods in cystic fibrosis.
        Front Pediatr. 2018; 6: 133
        • Sonner Z.
        • Wilder E.
        • Heikenfeld J.
        • et al.
        The microfluidics of the eccrine sweat gland, including biomarker partitioning, transport, and biosensing implications.
        Biomicrofluidics. 2015; 9031301
        • Laguna T.A.
        • Lin N.
        • Wang Q.
        • et al.
        Comparison of quantitative sweat chloride methods after positive newborn screen for cystic fibrosis.
        Pediat Pulmonol. 2012; 47: 736-742
        • McColley S.A.
        • Elbert A.
        • Wu R.
        • et al.
        Quantity not sufficient rates and delays in sweat testing in US infants with cystic fibrosis.
        Pediatr Pulmonol. 2020; 55: 3053-3056
        • Rueegg C.S.
        • Kuehni C.E.
        • Gallati S.
        • et al.
        Comparison of two sweat test systems for the diagnosis of cystic fibrosis in newborns.
        Pediatr Pulmonol. 2019; 54: 264-272
        • Chakraborty P.
        • Potter B.K.
        • Hayeems R.Z.
        Maximizing benefits and minimizing harms: diagnostic uncertainity arising from newborn screening.
        Pediatrics. 2021; 148e2021052822
        • Linsdell P.
        Relationship between anion binding and anion permeability revealed by mutagenesis within the cystic fibrosis transmembrane conductance regulator chloride channel pore.
        J Physiol. 2001; 531: 51-66
        • Nori de Macedo A.
        • Mathiaparanam S.
        • Brick L.
        • et al.
        The sweat metabolome of screen-positive cystic fibrosis infants: Revealing mechanisms beyond impaired chloride transport.
        ACS Cent Sci. 2017; 23: 904-913
        • Hanssens L.S.
        • Duchateau J.
        • Casimir G.J.
        • protein C.
        Not just a chloride channel?.
        Cells. 2021; 10: 2844
        • Quinton P.M.
        The neglected ion: HCO3−.
        Nat Med. 2001; 7: 92-293
        • Kunzelmann K.
        • Schreiber R.
        • Hadorn H.B.
        Bicarbonate in cystic fibrosis.
        J Cyst Fibros. 2017; 16: 653-662
        • Bijman J.
        • Quinton P.M.
        Lactate and bicarbonate uptake in the sweat duct of cystic fibrosis and normal subjects.
        Pediatr Res. 1987; 21: 79-82
        • Nori de Macedo A.
        • Teo K.
        • Mente A.
        • et al.
        A robust method for iodine status determination in epidemiological studies by capillary electrophoresis.
        Anal Chem. 2014; 286: 10010-10015
        • Saoi M.
        • Percival M.
        • Nemr C.
        • et al.
        Characterization of the human skeletal muscle metabolome for elucidating the mechanisms of bicarbonate ingestion on strenuous interval exercise.
        Anal Chem. 2019; 91: 4709-4718
        • Jadoon S.
        • Karim S.
        • Akram M.R.
        • et al.
        Recent developments in sweat analysis and its applications.
        Int J Anal Chem. 2015; 2015164974
        • Herrmann F.
        • Mandol L.
        Studies of pH of sweat produced by different forms of stimulation.
        J Invest Dermatol. 1955; 24: 225-246
        • Kleyn M.
        • Korzeniewski S.
        • Grigorescu V.
        • et al.
        Predictors of insufficient sweat production during confirmatory testing for cystic fibrosis.
        Pediatr Pulmonol. 2011; 46: 23-30
        • Kubán P.
        • Greguš M.
        • Pokojová E.
        • et al.
        Double opposite end injection capillary electrophoresis with contactless conductometric detection for simultaneous determination of chloride, sodium and potassium in cystic fibrosis diagnosis.
        J Chromatogr A. 2014; 1358: 293-298
        • Ďurč P.
        • Foret F.
        • Pokojová E.
        • et al.
        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.
        Anal Bioanal Chem. 2017; 409: 3507-3514
        • Marvelli A.
        • Campi B.
        • Mergni G.
        • et al.
        Sweat chloride assay by inductively coupled plasma mass spectrometry: a confirmation test for cystic fibrosis diagnosis.
        Anal Bioanal Chem. 2020; 412: 6909-6916
        • Park H.W.
        • Nam J.H.
        • Kim J.Y.
        • et al.
        Dynamic regulation of CFTR bicarbonate permeability by [Cl-]i and its role in pancreatic bicarbonate secretion.
        Gastroenterology. 2010; 139: 620-631