Issues in newborn screening for phenylketonuria.

The blood sample for phenylketonuria (PKU) screening should be obtained at least 12 hours after the infant's birth. Newborn screening for PKU has largely eliminated mental retardation caused by this disease. If the first phenylalanine test demonstrates positive results, a repeat test should be performed. Treatment to prevent sequelae from this disorder is best carried out in cooperation with an experienced PKU center. Dietary care is expensive, and financial assistance may be necessary for many families. A phenylalanine-restricted diet should be started as soon as possible. Occasionally, cases of PKU are missed by newborn screening. Thus, a repeat PKU test should be performed in an infant who exhibits slow development.