Phenylalanine

Phenylalanine is an essential amino acid found in protein-rich foods. This urine test measures 24-hour phenylalanine excretion and screens for phenylketonuria (PKU), an inherited metabolic disorder where the body cannot properly break down phenylalanine. PKU causes intellectual disability if undetected and untreated in infancy. Elevated urinary phenylalanine indicates high blood phenylalanine levels, requiring a specialized low-phenylalanine diet. Most newborns are screened for PKU at birth, but this test may be used in older children or adults with suspected metabolic disease or developmental concerns.