cysteine measurements during total parenteral nutrition

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Abstract
Using a method that measures plasma protein-bound ½ cystine, plasma free cyst(e)ine, and urine free cyst(e)ine, we have observed that infants receiving total parenteral nutrition supplemented with cysteine-HCl have significantly higher plasma and urine free cyst(e)ine concentrations (11.3 ± 3.4 µm/dl and 47.2 ± 24.0 µm/dl, x̄ ± SD) than when ½ cystine concentrations are measured by automated amino acid analysis (7.4 ± 2.0 µm/dl, plasma and 25.0 ± 7.0 µm/dl, urine). These data suggest that both the sulfhydryl and disulfide form of cyst(e)ine must be measured to asses the effect of cysteine-HCl supplemented total parenteral nutrition.