Accuracy of the sweat test: advantage of a micromethod.

The high sweat electrolyte concentration in cystic fibrosis is most important in the diagnosis of this disease. The method used for its determination should be simple to perform, harmless to the patient, and accurate. The widely-used method of collecting sweat on a filter paper (Shwachman, Leubner, and Catzel, 1955) after pilocarpine iontophoresis (Gibson and Cooke, 1959) fulfils the first two conditions but not the latter. Both weighing and elution may introduce serious errors, and the method is known to be unreliable for samples weighing under 20 mg. Moreover, the sweat sample is not transportable and has to be analysed rapidly in order to avoid evaporation. A simple, harmless, and accurate method of collecting and estimating sweat electrolyte concentration is described, which has given satisfactory results for over three years (de Haller, Siegenthaler, Hampal, Spahr, Vulliet, and Favre, 1962; Siegenthaler, de Haller, de Haller, Hampal, and Muller, 1964).