Measurement of osmolality and sodium concentration in heated-cup sweat collections for the investigation of cystic fibrosis.

A new system (Wescor) for sweat collection and analysis was examined with respect to its suitability for the investigation of children suspected to have cystic fibrosis. The effects of iontophoresis current, sweat collection time, sweat storage and analysis were examined, and as a result the technique was modified to allow collection and storage of sufficient sweat for sodium and potassium as well as osmolality assays in 10-20 minutes. The small electrodes and speed of the procedure make it practical for use with small children, with a reproducibility of 13-24% (coefficient of variation for whole procedure).