Improved sweat test method for the diagnosis of cystic fibrosis.

We describe a new technique of collecting sweat for measurement of osmolality and sodium concentrations. Eighty two subjects were studied--39 controls and 43 patients with cystic fibrosis. Adequate amounts of sweat were obtained in 81 subjects and sweat was analysed for both osmolality and sodium concentrations in 73 subjects. The 34 controls gave sweat osmolality and sodium values ranging from 62 to 196 mmol/kg and 9 to 72 mmol/l respectively. The 39 cystic fibrosis patients gave osmolality values ranging from 220 to 416 mmol/kg and sodium concentrations ranging from 60 to 150 mmol/l. Sweat osmolality alone was determined in eight infants under 50 days of age--four later developed the clinical features of cystic fibrosis and four, in whom cystic fibrosis was suspected, were later excluded. Sweat osmolality values in these two groups ranged from 255 to 345 mmol/kg and 87 to 123 mmol/kg respectively. The simplicity of collecting sweat and the measurement of osmolality offer distinct advantages over techniques previously described.