Studies were included if they met the following criteria: (1) randomized controlled trials, cohort studies, or clinical trials assessing metabolomic biomarkers in patients with HF; (2) use of validated metabolomic platforms (e.g., LC-MS, GC-MS, or NMR spectroscopy); and (3) reporting of associations between metabolite levels and clinical outcomes such as NT-proBNP, six-minute walk distance (6MWD), hospitalization, or mortality. The gene discussed is NPPB; the disease is hydrops fetalis.