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

Abstract

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.

Keywords: Compact electrolyte analyzers; Horiba; regional sweat collection; sweat patches.

Figure 1.

Sample extraction and analysis scheme.

Figure 2.

Regression of CENTRIFUGE HORIBA (centrifuge sweat extraction, compact Horiba B‐722 analysis), SYRINGE HPLC (syringe sweat extraction, ion chromotography analysis), and SYRINGE HORIBA (combined field technique using syringe sweat extraction and compact Horiba B‐722 analysis) on CENTRIFUGE HPLC (reference laboratory technique using centrifuge sweat extraction and ion chromatography analysis) for sweat [Na⁺]. n = 210. Dashed line is the line of identity.

Figure 3.

Regression of CENTRIFUGE HORIBA (centrifuge sweat extraction, compact Horiba B‐731 analysis), SYRINGE HPLC (syringe sweat extraction, HPLC analysis), and SYRINGE HORIBA (combined field technique using syringe sweat extraction and compact Horiba B‐731 analysis) on CENTRIFUGE HPLC (reference laboratory technique using centrifuge sweat extraction and ion chromatography analysis) for sweat [K⁺]. n = 116. Dashed line is the line of identity.