Tryptophan and Its Derived Metabolites as Biomarkers for Tuberculosis Disease: A Systematic Review.

Feasible diagnostic assays are required to detect new TB cases and monitor treatment. This study aimed to evaluate evidence on Trp and its metabolites as proposed biomarkers for TB. Through specific keyword searches, we identified 170 relevant literature sources and included seven publications (from 2013 to 2023). The biomarker used in these studies were IDO activity, IDO-1 gene expression, and plasma IDO protein, measured using ELISA, LC-MS, UPLC, and transcriptional profiling. The studies encompassed a pediatric case-control and six studies involving adults, pregnant women with TB-HIV, and individuals with MDR-TB, active TB, and latent TB. The assessment of IDO activity and IDO protein level demonstrated promising performance in distinguishing active TB from controls and in evaluating treatment failure and recurrent cases to controls. Trp and its metabolites fulfilled nearly all of TPP criteria for detecting active TB. This study highlights the potential of utilizing host Trp and its metabolites as non-sputum-based biomarker for TB infection.