Measurement of sodium concentration in sweat samples: comparison of 5 analytical techniques

Abstract

Sweat sodium concentration (SSC) can be determined using different analytical techniques (ATs), which may have implications for athletes and scientists. This study compared the SSC measured with 5 ATs: ion chromatography (IChr), flame photometry (FP), direct (DISE) and indirect (IISE) ion-selective electrode, and ion conductivity (IC). Seventy sweat samples collected from 14 athletes were analyzed with 5 instruments: the 883 Basic IC Plus (IChr, reference instrument), AAnalyst 200 (FP), Cobas 6000 (IISE), Sweat-Chek (IC), and B-722 Laqua Twin (DISE). Instruments showed excellent relative (intraclass correlation coefficient (ICC) ≥ 0.999) and absolute (coefficient of variation (CV) ≤ 2.6%) reliability. Relative validity was also excellent between ATs (ICC ≥ 0.961). In regards to the inter-AT absolute validity, compared with IChr, standard error of the estimates were similar among ATs (2.8-3.8 mmol/L), but CV was lowest with DISE (3.9%), intermediate with IISE (7.6%), and FP (6.9%) and highest with IC (12.3%). In conclusion, SSC varies depending on the AT used to analyze samples. Therefore, results obtained from different ATs are scarcely comparable and should not be used interchangeably. Nevertheless, taking into account the normal variability in SSC (∼±12%), the imprecision of the recommendations deriving from FP, IISE, IC, and DISE should have trivial health and physiological consequences under most exercise circumstances.

Normative data for sweating rate, sweat sodium concentration, and sweat sodium loss in athletes: An update and analysis by sport

“…The results of this study could help guide education for coaches and sport staff when developing training plans to ensure that adequate fluid breaks are available and that the appropriate hydration (fluid with varying levels of electrolytes) is accessible throughout training and competition, especially those done at higher intensities, for longer durations, and in the hotter months or geographical areas. Practitioners or researchers interested in testing their own athletes are referred to previously published literature regarding practical procedures for sweating rate and/ or sweat [Na + ] testing (Armstrong & Casa, 2009;Baker, 2017;Goulet, Asselin, Gosselin, & Baker, 2017).…”

Physiological mechanisms determining eccrine sweat composition

“…Because of differences in ease of use and equipment cost, a wide range of analytical techniques have been used by scientists and practitioners to measure sweat composition (Baker 2017). However, caution should be used when comparing results across the literature because sweat [Na + ] varies significantly among common analytical techniques; in general, ion conductivity > flame photometry ≥ indirect ion-selective electrode > direct ion-selective electrode ≥ ion chromatography (Baker et al 2014;Boisvert and Candas 1994;Dziedzic et al 2014;Goulet et al 2017Goulet et al , 2012. One study directly compared sweat [Na + ] analyzed with all five different techniques (Goulet et al 2017).…”

“…However, caution should be used when comparing results across the literature because sweat [Na + ] varies significantly among common analytical techniques; in general, ion conductivity > flame photometry ≥ indirect ion-selective electrode > direct ion-selective electrode ≥ ion chromatography (Baker et al 2014;Boisvert and Candas 1994;Dziedzic et al 2014;Goulet et al 2017Goulet et al , 2012. One study directly compared sweat [Na + ] analyzed with all five different techniques (Goulet et al 2017). While all techniques had low within-method variability (CVs ≤ 2.6%), there was significant variability between techniques, with ion conductivity producing sweat [Na + ] values most different (CV = 12.3%) from the reference ion chromatography method (Goulet et al 2017).…”

“…One study directly compared sweat [Na + ] analyzed with all five different techniques (Goulet et al 2017). While all techniques had low within-method variability (CVs ≤ 2.6%), there was significant variability between techniques, with ion conductivity producing sweat [Na + ] values most different (CV = 12.3%) from the reference ion chromatography method (Goulet et al 2017). Sweat [Cl − ] and [K + ] have been assessed in only a few studies, but follow a similar pattern as [Na + ] with respect to differences among analytical techniques (Baker et al 2014;Boisvert and Candas 1994).…”

“…The day-to-day CV for sweat [K + ] is 6-19% (Baker et al 2009). Assuming that ~ 1 to 5% of this CV is due to intra-instrument variability (Baker et al 2014;Boulyga et al 2007;Doorn et al 2015;Goulet et al 2017Goulet et al , 2012Pullan et al 2013), this suggests that the remaining up to ~ 5 to 14% CV is probably due to physiological variability.…”