Measurement of Sweat Sodium Concentration in Patients With Chronic Kidney Disease

It has been shown that excretion of sodium and water through the skin in the form of sweat represents a regulatory mechanism of electrolyte- and fluid balance. Since patients with chronic kidney disease (CKD) exhibit increased skin sodium content, we investigated the feasibility of sweat testing as a novel experimental tool to a more complete assessment of fluid- and sodium homeostasis.

In this cross-sectional feasibility study, we applied pilocarpine iontophoresis to induce sweat testing in 58 patients across various stages of CKD including patients after kidney transplantation as well as a healthy control cohort (n=6) to investigate possible effects of CKD and transplantation status on sweat rate and sodium concentration. Due to non-linear relationships, we modeled our data using polynomial regression.

Decline of kidney function showed a significant association with lower sweat rates: adj R²= 0.2278, F(2, 61) = 10.29, p = 0.000141. Sweat sodium concentrations were increased in moderate CKD, however this effect was lost in end stage renal disease: adj R² = 0.3701, F(4, 59) = 10.26, p = 2.261e-06. We observed higher sweat weight in males compared to females.

Diagnostic sweat analysis represents an innovative and promising noninvasive option for more thorough investigation of sodium- and fluid homeostasis in CKD patients. Lower sweat rates and higher sweat sodium concentrations represent a unique feature of CKD patients with potential therapeutic implications.