Why is newborn screening used to detect phenylketonuria early?

Newborn screening for phenylketonuria (PKU) is critical because it allows for the early detection and intervention of a serious inborn error of metabolism before irreversible damage occurs.12

PKU is caused by a deficiency in the enzyme phenylalanine hydroxylase, which leads to the accumulation of the amino acid phenylalanine in the body. If left untreated, these high levels interfere with metabolic processes in the central nervous system, resulting in severe consequences such as intellectual disability, seizures, and behavioral abnormalities.34

By using a simple blood-screening test—often called the Guthrie test—during the first week of life, clinicians can identify affected infants and immediately implement a strict, low-phenylalanine diet. This early dietary intervention is highly effective; it prevents the accumulation of toxic levels of phenylalanine, thereby allowing children with PKU to avoid intellectual disability and grow into healthy, productive adults.124