# Full Validation and Application to Clinical Research of a High-Performance Liquid Chromatography Method for the Assessment of Urinary 3-Indoxyl Sulfate in Pediatric Patients with Hematopoietic Stem Cell Transplant

## TL;DR

This paper validates a method to measure 3-indoxyl sulfate in urine from pediatric patients after stem cell transplants, aiming to assess gut health and clinical outcomes.

## Contribution

The study introduces a validated HPLC-FLD method for quantifying 3-IS in pediatric urine samples, filling a gap in microbiome health assessment after HSCT.

## Key findings

- The HPLC-FLD method is linear, accurate, and precise for 3-IS quantification in urine.
- 3-IS stability was confirmed under various storage conditions, including freeze-thaw cycles and long-term freezing.
- The method was successfully applied to quantify 3-IS in pediatric HSCT patient urine samples.

## Abstract

3-indoxyl sulfate (3-IS) results from a hepatic transformation of indole, a tryptophan degradation product produced by commensal gut bacteria. The metabolite has shown promise as a biomarker of dysbiosis and clinical outcomes following hematopoietic stem cell transplant (HSCT) in adults. Nonetheless, there is a paucity of data regarding microbiome health and outcomes in the pediatric HSCT setting. We developed and thoroughly validated an affordable high-performance liquid chromatography/fluorescence detector (HPLC-FLD) method to quantify 3-IS in urine for use in the pediatric setting. Chromatographic separation was achieved on a C18 column (250 × 4.6 mm × 5 μm) with a mobile phase consisting of pH 4.0 acetic acid-triethylamine buffer and acetonitrile (88:12, v/v), eluted isocratically at 1 mL/min. 3-IS fluorescence detection was set at excitation/emission of 280 and 375, respectively. The method was fully validated according to FDA-specified limits including selectivity, linearity (0.10 to 10.00 mg/L, r2 > 0.997), intra- and inter-day accuracy, and precision. 3-IS stability was confirmed after three freeze–thaw cycles, for short- and medium-term on a benchtop and at 4 °C and for long-term up to 60 days at −20 °C. The validated method was used to quantify 3-IS in urine samples from HSCT pediatric patients.