Sweat Sodium, Potassium, and Chloride Concentrations Analyzed Same Day as Collection Versus After 7 Days Storage in a Range of Temperatures

Abstract

The purpose of this study was to determine the effect of storage temperature on sodium ([Na]), potassium ([K]), and chloride ([Cl]) concentrations of sweat samples analyzed 7 days after collection. Using the absorbent patch technique, 845 sweat samples were collected from 39 subjects (32 ± 7 years, 72.9 ± 10.5 kg) during exercise. On the same day as collection (PRESTORAGE), 609 samples were analyzed for [Na], [Cl], and [K] by ion chromatography (IC) and 236 samples were analyzed for [Na] using a compact ion-selective electrode (ISE). Samples were stored at one of the four conditions: -20 °C (IC, n = 138; ISE, n = 60), 8 °C (IC, n = 144; ISE, n = 59), 23 °C (IC, n = 159; ISE, n = 59), or alternating between 8 °C and 23 °C (IC, n = 168; ISE, n = 58). After 7 days in storage (POSTSTORAGE), samples were reanalyzed using the same technique as PRESTORAGE. PRESTORAGE sweat electrolyte concentrations were highly related to that of POSTSTORAGE (intraclass correlation coefficient: .945-.989, p < .001). Mean differences (95% confidence intervals) between PRESTORAGE and POSTSTORAGE were statistically, but not practically, significant for most comparisons: IC [Na]: -0.5(0.9) to -2.1(0.9) mmol/L; IC [K]: -0.1(0.1) to -0.2(0.1) mmol/L; IC [Cl]: -0.4(1.4) to -1.3(1.3) mmol/L; ISE [Na]: -2.0(1.1) to 1.3(1.1) mmol/L. Based on typical error of measurement results, 95% of the time PRESTORAGE and POSTSTORAGE sweat [Na], [K], and [Cl] by IC analysis fell within ±7-9, ±0.6-0.7, and ±9-13 mmol/L, respectively, while sweat [Na] by ISE was ±6 mmol/L. All conditions produced high reliability and acceptable levels of agreement in electrolyte concentrations of sweat samples analyzed on the day of collection versus after 7 days in storage.

Physiological mechanisms determining eccrine sweat composition

“…Differences in sample storage temperature seem to have minimal impact on sweat electrolyte concentrations, as (Baker et al 2018a) found negligible changes in sweat [Na + ], [Cl − ], and [K + ] between same-day analysis and post-7-day storage (in Parafilm-M ® -sealed vials) at − 20 °C, 8 °C, and 23 °C. There is a paucity of research measuring the effect of storage conditions on other sweat constituents.…”

“…Sample storage methodology is another potential source of variability in sweat constituent concentrations and, not surprisingly, one of the most important factors is proper sealing of the sample vials. When well-sealed and stored at room temperature (23-25 °C), refrigeration (4-8 °C), or frozen (− 20 °C) for up to 7 days, minimal sweat evaporation and minimal change in sweat [Na 2+ ], [Cl − ], and [K + ] has been reported (Baker et al 2018a;Bergeron et al 2011;Jones et al 2008). However, when vials were capped but not sealed with Parafilm-M ® for 3 or 5 days, 19% and 32% sample evaporation has occurred; storing the vials in a plastic bag was associated with 16 and 27% sample evaporation, respectively.…”

The effect of sweat sample storage condition on sweat content

“…Therefore, samples are sometimes stored at room temperature until chemical analysis. The selected storage durations (0, 7, 28 days) were chosen to allow for comparison with previous research [ 11 ]. In addition, storage for 7 days is a realistic time span for field work and 28 days was selected to determine the impact of a significantly longer storage duration.…”

“…Whilst several studies have described the best techniques for sweat collection and subsequent chemical analysis [ 8–10 ], the best practices for sweat sample storage are yet to be quantified. It has been suggested that the use of inconsistent storage conditions (i.e., temperature and duration) can lead to substantial errors [ 11–14 ]. Dziedzic et al [ 12 ] reported a ≤ 14% increase in sweat sodium concentration when analyzed immediately after sampling compared to after refrigeration at 7°C for 7 days.…”

“…Therefore, sweat samples should be sealed or at least it should be reported whether sealing was adhered to [ 9 ]. More recently, Baker et al [ 11 ] concluded that sodium, chloride and potassium concentrations decreased significantly after 7 days of storage at a range of temperatures (−20°C, 8°C, 23°C, and an alternation of 8°C and 23°C to simulate sample transport from the field to the laboratory). Lastly, guidelines for the diagnosis of cystic fibrosis through chloride testing in sweat recommend sample storage for a maximum of three days at 4°C in the event a sample cannot be analyzed immediately [ 15 , 16 ].…”