title: The significance of sweat Cl/Na ratio in patients with borderline sweat test.
abstract: Recently a few cystic fibrosis (CF) patients with borderline or normal sweat tests have been reported. These patients present a diagnostic challenge. We aimed to study the sweat Cl/Na ratio in cystic fibrosis patients and to assess whether this ratio could be used as a diagnostic criteria. The mean sweat Cl/Na ratio of 3 groups was compared: Group A: 71 CF patients carrying 2 mutations known to be associated with severe disease presentation (delta F508, W1282X, G542X, N1303K, 1717-1G --> A). Group B: 10 compound heterozygous patients who carry one mutation associated with mild clinical disease (3849 + 10 kb --> T). Group C: 142 normal subjects. Sweat chloride levels higher than those of sodium were found in 96% of patients in Group A as compared to 3% of patients in Group C. In Group B 40% of the patients had sweat chloride levels higher than or equal to sodium levels. The mean Cl/Na ratio of Group A (1.2 +/- 0.1) differed significantly from that of Group B (0.94 +/- 0.1) and both groups had significant higher mean Cl/Na ratio compared to Group C (0.7 +/- 0.4) (P < 0.001). Thus in individuals with a borderline sweat test and a Cl/Na ratio > or = 1 the diagnosis of CF should be considered. However, a Cl/Na ratio < 1 does not exclude CF, since patients carrying mild mutations may have sweat sodium levels higher than those of chloride. Our findings suggest that the sweat Cl/Na ratio in CF is genetically determined and it may be of help in establishing the diagnosis of CF in patients with a borderline sweat test.
authors.affiliation: Department of Pediatrics, Chaim Sheba Medical Center, Ramat Gan, Israel.
authors.forename: A
authors.initials: A
authors.lastname: Augarten
authors.forename: S
authors.initials: S
authors.lastname: Hacham
authors.forename: E
authors.initials: E
authors.lastname: Kerem
authors.forename: B
authors.initials: B
authors.lastname: Sheva Kerem
authors.forename: A
authors.initials: A
authors.lastname: Szeinberg
authors.forename: J
authors.initials: J
authors.lastname: Laufer
authors.forename: R
authors.initials: R
authors.lastname: Doolman
authors.forename: R
authors.initials: R
authors.lastname: Altshuler
authors.forename: H
authors.initials: H
authors.lastname: Blau
authors.forename: L
authors.initials: L
authors.lastname: Bentur
mesh_terms: D002648:Child; D002712:Chlorides / Q000032:analysis*; D003550:Cystic Fibrosis / Q000235:genetics / Q000503:physiopathology*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics; D006801:Humans; D009154:Mutation; D012964:Sodium / Q000032:analysis*; D013542:Sweat / Q000737:chemistry*
chemical_list: C505032:CFTR protein, human; D002712:Chlorides; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D012964:Sodium