Increased sweat sulfate concentrations in chronic renal failure.

Inorganic sulfate concentrations are markedly elevated in patients with chronic renal failure (CRF). During hemodialysis, sulfate is removed and circulating levels drop significantly, while chloride concentrations remain relatively constant. We measured sulfate and chloride in sweat from CRF patients collected by pilocarpine iontophoresis. Sweat sulfate concentrations in uremic patients were significantly increased (404 +/- 43 vs. 105 +/- 6 microM in 22 controls). The correlation between plasma and sweat SO4 concentrations in CRF patients was significant (r = 0.77, P less than 0.01). However, the fractional excretion of sulfate in sweat (the sweat/serum ratio) was close to that of chloride (0.26 +/- 0.01 vs. 0.19 +/- 0.02) and was essentially the same before and after dialysis (0.20 +/- 0.01 vs 0.23 +/- 0.01) despite the significant absolute change in the extracellular SO4 concentration (from 2,018 +/- 153 to 709 +/- 21 microM) and no change in chloride concentrations. In patients with CRF, we conclude that the handling of inorganic sulfate by the sweat gland is not significantly different from that for chloride. Hemodialysis reduces absolute sulfate excretion markedly and thus may reduce the likelihood of forming calcium sulfate complexes in the sweat secretions. This could be a significant factor in the dialysis-related pruritus that has been ascribed to excess calcium deposition in the skin.