Quantification of Tryptophan, Indole, and Indoxyl Sulfate in Urine Using Liquid Chromatography-Tandem Mass Spectrometry.

Having a diverse gut microbiota has been correlated with the short- and long-term success of allogeneic stem cell transplantation. Intestinal bacteria metabolize the amino acid tryptophan to indole. Indole is further oxidized and sulfonated in the liver to 3-indoxyl sulfate (3-IS), which is then excreted in urine. Urinary 3-IS is a potential biomarker for intestinal health and an early predictor of successful stem cell transplantation. We describe a rapid method for quantifying tryptophan, indole, and 3-indoxyl sulfate in urine specimens, in which urine samples are diluted with a formic acid solution and deuterated internal standards, and then injected on LC-MS/MS for analysis.