Indirect measurements of sweat electrolyte concentration in the laboratory diagnosis of cystic fibrosis

AIM To investigate whether analytical methods based on the colligative physical chemical properties of ions or solutes in sweat are less effective than the specific measurement of electrolytes in the diagnosis of cystic fibrosis (CF). METHODS A single sweat sample was collected (Macroduct) from each of 211 infants and children, of whom 57 had CF, for the measurment of sodium, chloride, osmolality, and conductivity. RESULTS The ranges within which CF and non-CF individual values overlapped (equivocal ranges), were wider for sodium and osmolality measurement than for chloride or conductivity. Neither of the latter two measurements provided a discriminatory advantage over the other. The utilisation of broadly based age related ranges for non-CF control subjects served to improve the discriminatory power of all four measurements to an extent that, in this cohort, both chloride and conductivity provided complete discrimination. CONCLUSION Sweat conductivity is as effective as chloride measurement in the laboratory diagnosis of CF.

[1]  P. Farrell,et al.  Sweat chloride concentrations in infants homozygous or heterozygous for F508 cystic fibrosis. , 1996, Pediatrics.

[2]  M. Corey,et al.  Correlation of sweat chloride concentration with classes of the cystic fibrosis transmembrane conductance regulator gene mutations. , 1995, The Journal of pediatrics.

[3]  J. Kuzemko,et al.  Improved sweat test method for the diagnosis of cystic fibrosis. , 1984, Archives of disease in childhood.

[4]  S. Natelson,et al.  The Sweat Glands , 1975 .

[5]  D. Laroche,et al.  Abnormal frequency of ΔF508 mutation in neonatal transitory hypertrypsinaemia , 1991, The Lancet.

[6]  G. Cutting,et al.  The diagnosis of cystic fibrosis: a consensus statement. Cystic Fibrosis Foundation Consensus Panel. , 1998, The Journal of pediatrics.

[7]  R E COOKE,et al.  A test for concentration of electrolytes in sweat in cystic fibrosis of the pancreas utilizing pilocarpine by iontophoresis. , 1959, Pediatrics.

[8]  V. Legrys.  Sweat testing for the diagnosis of cystic fibrosis: practical considerations. , 1996, The Journal of pediatrics.

[9]  A Green,et al.  A Study of Sweat Sodium and Chloride; Criteria for the Diagnosis of Cystic Fibrosis , 1985, Annals of clinical biochemistry.

[10]  K B Hammond,et al.  Clinical evaluation of the macroduct sweat collection system and conductivity analyzer in the diagnosis of cystic fibrosis. , 1994, The Journal of pediatrics.

[11]  J. Kirk,et al.  Variation of Sweat Sodium and Chloride with Age in Cystic Fibrosis and Normal Populations: Further Investigations in Equivocal Cases , 1992, Annals of clinical biochemistry.

[12]  P. Quinton,et al.  The sweat gland , 1993 .

[13]  D. Stableforth,et al.  Sweat Sodium and Chloride Concentrations—Essential Criteria for the Diagnosis of Cystic Fibrosis in Adults , 1990, Annals of clinical biochemistry.