On indications for treatment of the hyperphenylalaninemic neonate.

Of 488 006 neonates tested by Guthrie screening 58 showed values above 2.5 mg/100 ml. Thirty-two showed values between 2.5 mg/100 ml and 15 mg/100 ml. Eighteen of these infants appeared to have phenylketonuria (PKU) and fourteen to have persistent hyperphenylalaninemia (HPA). Neither the initial Guthrie test-value nor the confirmatory test were able to differentiate between these two conditions. Consequently a phenylalanine restricted diet is started in any child with serumphenylalanine values exceeding 10 mh/100 ml (605 micronmol/l). The data show that the course of the dietary tolerance of phenylalanine and a 24-hour phenylalanine load test will differentiate infants with PKU from those with HPA.