Validity and reliability of a field technique for sweat Na⁺and K⁺analysis during exercise in a hot-humid environment

Abstract

This study compared a field versus reference laboratory technique for extracting (syringe vs. centrifuge) and analyzing sweat [Na+] and [K+] (compact Horiba B‐722 and B‐731, HORIBA vs. ion chromatography, HPLC) collected with regional absorbent patches during exercise in a hot‐humid environment. Sweat samples were collected from seven anatomical sites on 30 athletes during 1‐h cycling in a heat chamber (33°C, 67% rh). Ten minutes into exercise, skin was cleaned/dried and two sweat patches were applied per anatomical site. After removal, one patch per site was centrifuged and sweat was analyzed with HORIBA in the heat chamber (CENTRIFUGE HORIBA) versus HPLC (CENTRIFUGE HPLC). Sweat from the second patch per site was extracted using a 5‐mL syringe and analyzed with HORIBA in the heat chamber (SYRINGE HORIBA) versus HPLC (SYRINGE HPLC). CENTRIFUGE HORIBA, SYRINGE HPLC, and SYRINGE HORIBA were highly related to CENTRIFUGE HPLC ([Na+]: ICC = 0.96, 0.94, and 0.93, respectively; [K+]: ICC = 0.87, 0.92, and 0.84, respectively), while mean differences from CENTRIFUGE HPLC were small but usually significant ([Na+]: 4.7 ± 7.9 mEql/L, −2.5 ± 9.3 mEq/L, 4.0 ± 10.9 mEq/L (all P < 0.001), respectively; [K+]: 0.44 ± 0.52 mEq/L (P < 0.001), 0.01 ± 0.49 mEq/L (P = 0.77), 0.50 ± 0.48 mEq/L (P < 0.001), respectively). On the basis of typical error of the measurement results, sweat [Na+] and [K+] obtained with SYRINGE HORIBA falls within ±15.4 mEq/L and ±0.68 mEq/L, respectively, of CENTRIFUGE HPLC 95% of the time. The field (SYRINGE HORIBA) method of extracting and analyzing sweat from regional absorbent patches may be useful in obtaining sweat [Na+] when rapid estimates in a hot‐humid field setting are needed.

Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability

“…No study, to the author’s knowledge, has directly compared all methods, but a synopsis of the literature suggests that sweat [Na + ] is generally highest with conductivity and FP, intermediate with ISE, and lowest with IC. For example, in separate studies, conductivity produced approximately 6% higher sweat [Na + ] values than FP [124], FP values were approximately 20% higher than ISE [18] and IC [96], and ISE values were approximately 4% [125] and approximately 10% [126] higher than IC.…”

“…ISE techniques, while a measure of ion activity rather than a direct measure of concentration, are considered acceptable for CF diagnosis [122, 127, 133]. Studies measuring sweat [Na + ] have found that ISE (via a compact Na + analyzer; HORIBA Scientific, Irivine, CA, USA) has similar reliability to that of IC (CVs approximately 1–4% for both methods) [125, 126]. These studies also reported that compared with IC, the ISE technique produced sweat [Na + ] values with a mean bias of approximately 2–4 mmol/L (or approximately 4–10%) [125, 126].…”

“…Studies measuring sweat [Na + ] have found that ISE (via a compact Na + analyzer; HORIBA Scientific, Irivine, CA, USA) has similar reliability to that of IC (CVs approximately 1–4% for both methods) [125, 126]. These studies also reported that compared with IC, the ISE technique produced sweat [Na + ] values with a mean bias of approximately 2–4 mmol/L (or approximately 4–10%) [125, 126]. This small but significant discrepancy between ISE and IC could be due to the limited measurement resolution and range of ISE [125, 126, 129].…”

“…These studies also reported that compared with IC, the ISE technique produced sweat [Na + ] values with a mean bias of approximately 2–4 mmol/L (or approximately 4–10%) [125, 126]. This small but significant discrepancy between ISE and IC could be due to the limited measurement resolution and range of ISE [125, 126, 129]. Another potential drawback of ISE is the need for larger sample volumes compared with IC and ICP-MS [126, 129].…”

“…This small but significant discrepancy between ISE and IC could be due to the limited measurement resolution and range of ISE [125, 126, 129]. Another potential drawback of ISE is the need for larger sample volumes compared with IC and ICP-MS [126, 129]. However, investigators should weigh the shortcomings of sweat analysis in the field versus the potential error (e.g.…”