Early diagnosis of cystic fibrosis by means of sweat microosmometry.

A modified sweat test procedure was studied to evaluate its practicability in the diagnosis of cystic fibrosis in newborn infants. By means of vapor pressure osmometry, we measured sweat osmolality in 131 healthy children and 63 patients with CF. Reference values were determined according to age: healthy infants 4 to 9 days of age; 121 +/- 23 mmol/kg (mean +/- SD); healthy infants 10 days to 2 months, 109 +/- 13 mmol/kg; healthy infants 2 to 12 months, 86 +/- 13 mmol/kg; and healthy children and adults 2 to 23 years, 105 +/- 14 mmol/kg. The mean of corresponding values for the 63 patients with CF was 267 +/- 34 mmol/kg. There was no overlap of values in any age group, even when the 2 SD limit was taken into account. Thus the diagnosis of CF can be made by means of this approach in newborn infants 8 days of age or older.