Used in clinical diagnostics to detect phenylketonuria (PKU), a genetic disorder where the body cannot properly metabolize phenylalanine. Elevated levels of phenylpyruvic acid in urine indicate impaired phenylalanine hydroxylase activity, often detected via tests like the ferric chloride assay. It serves as a biomarker in diagnostic testing for PKU, particularly in confirmation of newborn screening results that measure phenylalanine levels. Also used in research settings to study metabolic pathways, enzyme deficiencies related to amino acid metabolism, and its potential roles in neurotoxicity, the nervous system, and inflammation in animal models.