Authentic human data for C6–C5 metabolites in urine, plasma, ileal fluid and feces

This document is a compilation of published quantitative data obtained with authentic calibrants for the concentrations of C6–C5 metabolites (i.e. 5-phenylvaleric acids, 4-hydroxy-5-hydroxyphenylvaleric acids, phenylvalerolactones and the associated phase-2 conjugates) in human urine, plasma, ileal fluid and feces. The originating publications were identified by searching Web of Science, PubMed and Google Scholar up to May 2024.

Data originally reported on a mass/day or mass/volume basis have been converted to a molar basis to facilitate comparisons, but some published data were excluded from these tables:

(i) Data originally reported relative to creatinine, the standard clinical practice with spot plasma and urine samples, cannot be accurately converted to a molar basis because creatinine production varies with sex, age and protein intake.
(ii) Data produced by acid or enzymic hydrolysis of phase-2 conjugates have not been tabulated except for glycine or glutamine conjugates when β-glucuronidase and sulfatase hydrolysis has been used.

Similar compilations have been prepared for C6–C1 metabolites (benzoic acids), C6–C2 metabolites (phenylacetic acids) and C6–C3 metabolites (3-phenylpropanoic acids and cinnamic acids) and the metabolites have been identified using the nomenclature recommended by Kay et al. (Kay et al. 2020) and are numbered consecutively in a single series through the five documents.