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Phenylketonuria (PKU) screening

Phenylketonuria is an autosomal recessive genetic metabolic disorder that greatly reduces the ability of those affected to metabolize phenylalanine, one of the amino acids in protein. A buildup of phenylalanine in the blood can cause profound damage to the central nervous system in children and adults. If untreated in newborns, PKU can cause irreversible brain damage within months. Lifelong treatment is required to prevent neurological and physical deterioration.

Who is at risk

Both the mother and father must have and pass on the defective gene. Most often, PKU is passed to children by two parents who are carriers of the disorder, but don't know it.


PKU signs and symptoms can be mild or severe and may include:

  • A musty odor in the breath, skin or urine, caused by too much phenylalanine in the body
  • Neurological problems that may include seizures
  • Skin rashes (eczema)
  • Fair skin and blue eyes, because phenylalanine can't transform into melanin — the pigment responsible for hair and skin tone
  • Abnormally small head (microcephaly)
  • Hyperactivity
  • Intellectual disability
  • Delayed development
  • Behavioral, emotional and social problems
  • Psychiatric disorders

What you can do

Consider genetic counseling if you have PKU or have a close relative with PKU. Be aware that most insurances do not pay for genetic counseling.

Preventive service at no cost

Screening for phenylketonuria in all newborns.

Why screening is important

Untreated PKU can lead to:

  • Irreversible brain damage and marked intellectual disability beginning within the first few months of life
  • Neurological problems such as seizures and tremors
  • Behavioral, emotional and social problems in older children and adults
  • Major health and developmental problems

What the screening is

Healthcare providers in a hospital draw a few drops of blood from a newborn's heel. The blood sample, which can be used to screen for other conditions as well, is tested in a laboratory to determine if it has too much phenylalanine in it.


Individuals with PKU must maintain a life-long protein-restricted diet while drinking a metabolic formula that provides the protein (minus phenylalanine) that is absent from their diet, along with other nutrients. Regular blood tests help determine whether the phenylalanine levels in the blood are within a safe range, and diets are adjusted to allow for changes through an individual’s life. There is one available medicine.

Additional tips

  • Food diaries or computer programs are available that list the amount of phenylalanine in baby foods, solid foods, PKU formulas, and common baking and cooking ingredients.
  • Encourage children with PKU to focus on sports, music or favorite hobbies, not on just what they can and can't eat.