ART4 and chronic kidney disease: 2019). In diabetes patients at various stages of CKD, a low level of tryptophan (<44.20 μmol/L) has been associated with a rapid decline in eGFR (Chou et al. 2018). Plasma analysis involving 3089 T2DM patients revealed associations between impaired kidney function, branched-chain and aromatic amino acids, and glycoprotein acetyls (Tofte et al. 2020). Recent experimental studies suggest that the presence of disordered GM-derived tryptophan metabolites serves as an indicator of renal injury (Liu et al. 2021).