Question

What is the normal range for phenylalanine levels in newborns? Do I need to have it rechecked?

Answer

The normal blood phenylalanine level in neonates with phenylketonuria (PKU) is below 120μmol/L. Depending on the severity of the condition, phenylalanine concentrations vary:

  • Typical PKU: Blood phenylalanine concentration greater than 1200μmol/L.
  • Moderate PKU: 360 to 1200μmol/L.
  • Mild PKU: Blood phenylalanine concentration below 120 to 360μmol/L. If the screening result is 1.9, it may indicate a mild form of PKU. In this case, treatment should be initiated as soon as possible, primarily through dietary therapy. Neonatal PKU screening is typically conducted on the third day after birth, involving the collection of heel cord blood. If the screening result shows a phenylalanine content greater than 0.24mmol/L (4mg/dl), which is twice the normal reference value, a recheck or venous blood quantification test is needed to determine the accurate levels of phenylalanine and tyrosine.