Validity of the Wescor's sweat conductivity analyzer for the assessment of sweat electrolyte concentrations

The purpose of this study was to compare the "NaCl equivalent" values determined by the Wescor's sweat conductivity analyzer (Sweat-Chek) with the sweat Na+ and Cl- concentration values measured by conventional methods. The sweat was induced by 60-min exercise and collected by a closed-pouch collector. The "NaCl equivalent" values determined by the sweat conductivity analyzer (mean: 75 mmol.L-1, range: 38 - 122, n = 72) were significantly (P < 0.05) greater than Na+ concentration values (mean: 71 mmol.L-1, range: 24 - 123, n = 72) measured by flame photometry and Cl-concentration values (mean: 61 mmol.L-1, range: 18 - 100, n = 48) measured by coulometric titration. The difference were most accentuated for low concentration values. The 95% confidence-agreement intervals around the mean differences between methods were 11 mmol.L-1 (14%) for both Na+ and Cl-. The Sweat-Chek conductivity analyzer is a portable instrument which approximates the actual Na+ and Cl- concentrations in sweat but with a positive bias probably due to the other unmeasured anions present in sweat.