Phenylketonuria (PKU) Screening for a Newborn

Learn about the importance of Phenylketonuria (PKU) screening for newborns, how the test is conducted, and the health issues caused by this rare genetic disorder. Discover the various treatments and dietary guidelines to follow for PKU patients. Find out what to do as a parent if your child is diagnosed with PKU and how to help them manage the condition.

PKU affects one out of every 15,000 babies in the US, although it is less common in India. As a parent, it's important to be aware of this rare disease and the harm it can cause to your baby's developing brain. Even seemingly healthy babies should undergo a PKU test to detect the condition early.

In this article, we'll discuss the procedure for conducting the test, the health issues caused by PKU, and how you can help your child if they have the condition.

What Is A PKU Screening Test?

A blood test for PKU is given to newborns 24–72 hours after birth. Phenylketonuria (PKU) is a rare disorder where the body can't break down phenylalanine (Phe) found in foods and aspartame.

Eating these foods can lead to a buildup of Phe in the blood, causing long-term harm to the nervous system and brain.

Health issues linked to high Phe levels include seizures, psychiatric problems, and severe intellectual disability.

Why is it necessary to do this test?

If PKU isn't diagnosed and treated right away, it can lead to long-term complications, such as:

  • Delays in development
  • Hyperactivity
  • Lower IQ
  • Mental illness with severe consequences
  • Mood disturbances

Risk factors of PKU

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If both parents are carriers of the defective PKU gene, their child will be born with the disease if they receive one copy from each parent.

Each pregnancy has the following possibilities when both parents are carriers:

  • There is a 1 in 4 chance of having a child who is affected.
  • There's a 2 in 4 chance of having a carrier child.
  • There's a one-in-four chance of having a child who isn't a carrier.

What Is the Cause of PKU?

  • PKU is caused by an inherited defect in the gene that regulates the production of phenylalanine hydroxylase (PAH) enzymes.
  • The mutation in the PAH enzyme is responsible for the inability to convert phenylalanine to tyrosine, leading to the accumulation of phenylalanine in the body.
  • PKU is caused by a chromosomal mutation on chromosome 12, which varies in type and severity.
  • Phenylalanine makes up 5% of all-natural protein, and people with PKU cannot properly break it down due to the PAH enzyme deficiency.

What Are the Symptoms and Signs of PKU?

  • PKU is caused by the accumulation of too much phenylalanine in the body, which can lead to developmental delays and permanent intellectual disability if left untreated.
  • Children with PKU have fair skin, light hair, and blue eyes due to the effect of phenylalanine on melanin production.
  • Other symptoms of PKU may include:
  • Behavioral issues
  • Epilepsy
  • Growth and developmental issues
  • Skin rashes
  • A musty odor in the newborn's breath, skin, or urine.

PKU Diagnosed: When and how will the test be done?


  • A blood sample is taken within 24 hours of the baby's birth for newborn screening.
  • The heel-prick test or urine test is used to screen for PKU.
  • Results are based on the amount of phenylalanine in the blood and levels over 4 mg/dL are considered high.
  • False-positive or false-negative results are possible due to factors like prematurity, feeding issues, or medications.
  • Risks associated with a heel-prick test include bleeding, infection, and bruising.
  • The baby should be at least 24 hours old before the test is done, and parents should inform the doctor of any medications or supplements being taken if breastfeeding.

How Is Phenylketonuria Treated?

treated PKU babies are given special dietary instructions to continuously monitor and reduce phenylalanine levels.

  • PKU Formula for Babies and Kids:

A phenylalanine-free formula is necessary for PKU babies. PKU children can also be fed solid food with low phenylalanine levels.

  • Medical Nutrition Therapy:

PKU patients should follow a low-protein diet, avoid foods high in protein, and artificial sweeteners containing phenylalanine. Special formulas may be required at any age.

  • Amino Acid Remedy:

Supplements containing neutral amino acids are available in tablet and powder form, but should only be taken under a doctor's supervision.

  • PKU Medicines:

The FDA has approved the drug sapropterin to increase the body's phenylalanine tolerance levels, but it is taken in close collaboration with the PKU diet and not prescribed to everyone.

Prevention Strategic for PKU Babies

  • Ensure early treatment: Early treatment and a low-phenylalanine diet can prevent intellectual and physical restrictions.
  • Special formula: PKU babies require special milk formula and regular phenylalanine level monitoring through blood tests.
  • Follow diet guidelines: Stick to the diet plan and guidelines provided by the dietitian. Measure food portions with cups, spoons, and a scale.
  • Phenylalanine-free diet: A phenylalanine-free diet is necessary throughout life to avoid brain damage as the child grows.
  • Low protein foods: Low protein foods like bread, flour, rice, and pasta are readily available in retail food stores.
  • Experiment with food: Be creative with food while keeping PKU restrictions in mind. Consult with a dietitian for new ideas and meal variety.

Some Key Points for Parents to Remember

Living with a PKU child is difficult. Some strategies to consider are listed below.

  • Consult with your dietician or doctor to stay updated on PKU.
  • Encourage hobbies to promote your child's well-being, such as music or sports.
  • Connect with others dealing with PKU on social media or online groups to learn from their experiences.
  • Plan meals and snacks ahead of time for family events or outings to comply with PKU dietary restrictions.
  • Seek advice from a dietitian experienced in PKU to create low-phenylalanine meals for special occasions.
  • Involve your child in meal planning and encourage them to maintain a food tracker for health-conscious habits.
  • Check with the restaurant for PKU-friendly options or bring a home-cooked meal for your child.


PKU is a lifelong chronic disease, but with planning and guidance, you can make life easier for your child. Keep researching, consult regularly with your doctor and dietitian, track food intake, and test for PKU regularly to help your child live a healthy life.

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