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 the condition. It serves as a biomarker in newborn screening programs. Also used in research settings to study metabolic pathways involving aromatic amino acids. Its presence helps assess enzyme deficiencies and monitor dietary treatment efficacy in PKU patients.