Phenylketonuria (PKU) Test for a Newborn

Phenylketonuria (PKU) test, also known as PKU newborn screening or PKU metabolic screening, is one of the most common newborn tests performed in the United States. It is, in fact, mandatory in the United States and Canada. Babies who are born with Phenylketonuria inherit this genetic disease from their parents. It is an inherited defect in metabolism which results in reduced absorption of phenylalanine amino acid. It can lead to serious health issues. Read on to know more about the PKU test at birth, how a PKU blood test can help detect the disease and other relevant details.


What Is the Phenylketonuria (PKU) Test?

The Phenylketonuria (PKU) Test is performed to check if the newborn has PKU. This condition can result in severe damage to the brain, nervous system, cause intellectual disability and various other health problems. The issue generally occurs in the first year of the child’s life, causing the infant to be bizarrely sleepy and listless. They tend to develop red itchy rash and can experience difficulty feeding. Babies with PKU condition have lighter skin and hair than other family members and babies who do not have PKU condition.

Why Does a Baby Need the PKU Test?

1 in every 10,000 -15,000 babies born in the United States gets affected by PKU. Newborns must take the infant PKU test in the United States of America. Here is the answer to the commonly asked question, “Why is the PKU test so important?”

  • The baby will need to take the PKU Test because the sooner it is found, the sooner the treatment will begin.
  • Treatment will prevent the newborn from being intellectually disabled and other developmental issues in the child.
  • The PKU test is generally a part of the newborn screening series of tests conducted in the US to check if the newborn has high levels of Phe in blood.
  • Children and both younger and older infants adopted from other countries also need to go through the PKU test if they have or exhibit the symptoms of Phenylketonuria.

Causes of PKU in a Baby

PKU is a metabolic disorder and is an inherited congenital disability condition in newborn babies. The buildup of phenylalanine in the body causes PKU; the body uses this amino acid to break other proteins. As this is inherited, it essentially means that the defect has passed on from the parent to the child through genes. 

PKU is caused when there is a defect in the PAH gene in the body. The defect in the gene alters the way phenylalanine is broken down and absorbed by the body during digestion. When a parent has 1 mutated gene, they can pass PKU to the children. This means that both parents are carriers of the defective gene.


However, they necessarily do not have symptoms of PKU. Similarly, if the child inherits the PAH gene from just one parent, the child will undergo a gene change for PKU. The child will become a carrier of PKU while will not have diseases himself. This also makes PKU an autosomal recessive disease.


Signs and Symptoms of PKU in a Baby

When a newborn is neither diagnosed nor treated, phenylalanine may begin to build up in the baby’s bloodstream. The moment the phenylalanine level reaches the brain, it tends to cause irreversible damage to the brain, nervous system, tissues, and permanent damage to other organs. The PKU signs and symptoms can range from being very mild to extremely severe. Below is the list of signs and symptoms of PKU in a baby:


  • Neurological problems like seizures
  • Lighter skin, eyes, and hair color (Phenylalanine present in the body cannot transform into melanin. Melanin pigment is responsible for hair and skin color)
  • Skin rashes similar to eczema
  • Musty smell in the skin, breath, or urine caused due to excessive presence of phenylalanine in the baby’s body
  • Intellectual Disability
  • Microcephaly – unusually small size of the head
  • Hyperactive
  • Delayed development
  • Emotional, Behavior, and social problems
  • Taking a long time to crawl, sit or even walk
  • Bumpy movements in leg and arms
  • No interest in whatever is happening in the surroundings

Risks of the PKU Test

It is a needle stick test. Hence there is little or no risk to the baby. When the needle is poked in the baby’s heel, the baby will feel a little pinch. A very small bruise may occur at the point where the needle is pricked. This usually goes away pretty quickly. On rare occasions, there could be a little bleeding, infection, or possibly a sore.


When and How Is the PKU Test Done?

Phenylketonuria (PKU) Test is a blood test performed on newborns within 24 to 72 hours of their birth. The test should not be performed 24 hours after birth. The baby would have consumed some protein through the mother’s breastmilk or some other formula by this time. This helps to ascertain accurate test results. 


The PKU test screening is performed with a heel prick, needle stick test. The test is done by withdrawing a few drops of blood from the baby’s heel. Another alternative to heel prick is the urine test. The doctor will collect a sample of urine from the baby.

How to Get Your Child Ready for the PKU Test?

There is no special preparedness required for the child before the Phenylketonuria (PKU) Test. Ensure the healthcare provider is aware of all the medicines, vitamins, herbs, and other supplements the mother is consuming, as she would breastfeed the newborn. 


What Does PKU Test Results Mean?

The PKU test results can vary from one child to the other. These depend on the child’s age, gender, prior health history, the method of the test, and other factors. The test result of the child does not necessarily mean that there is a problem.  Consult with your health care provider to understand in detail what the test results mean for the child. 

As PKU is a genetic condition, the doctor may ask the parents and the baby to undergo a genetic test. If the test results are not normal, then the health care provider will advise performing more tests to confirm the test result or to be able to rule it out. It could be doing another set of urine tests and or blood tests. However, if the test results that come as normal were performed within 24 hours after the baby’s birth, your health care provider will advise you to do the tests again after the baby is at 1 -2 weeks of age.


The PKU diagnostic test determines the presence of phenylalanine in the blood. The normal reference range of phenylalanine in the blood is supposed to be less than 2 mg/dl (milligrams per deciliter). It is considered high when the test result shows more than 4 mg/dl of phenylalanine in the blood. This means that the child has PKU. The test will again be repeated once the baby is 7 to 14 days old.

What Factors Can Affect a Child’s PKU Test Results?

Different factors can affect Child’s PKU Test Results. Some of the common factors are listed below:


  • The blood test has a possibility of giving a false-negative or a false-positive result in some cases.
  • PKU test results through urine tests can get affected due to intake of antibiotic medicines like aspirin
  • When the baby is refusing to eat or is vomiting, in such situations, PKU tests performed can give a false-negative result. The baby needs to have eaten properly for 2 days before the tests are performed to get the correct result.
  • The baby is born premature (early). This factor can lead to a false-positive result as some liver enzymes in the baby would not have completely developed.
  • A baby born with less weight for about 5lbs may not have Phenylketonuria (PKU). However, it may have very high levels of phenylalanine.
  • If a baby has been drinking milk for less than 24 hours, doing a test can lead to incorrect results. Hence it is important that the baby has been breastfeeding or has taken formula for at least 2 complete days.

Treatment for PKU in Babies

Babies born with PKU are treated with special dietary specifications. This is to check and reduce the levels of phenylalanine continuously. The ways to treat the babies with PKU are as follows:

1. Primary Treatment

  • A proper diet plan with very restricted consumption of protein, as food with protein, contain phenylalanine
  • Newborns tested positive with PKU are put on a PKU formula immediately (PKU formula is a dietary nutritional supplement without phenylalanine. However, it has other essential nutrients and proteins required for the baby’s growth)

2. Food to Avoid

  • It is extremely important to avoid any high-protein food to keep in check the levels of phenylalanine.
  • Red meat like beef and pork, chicken, fish, eggs, milk, cheese, beans, and soybeans should be avoided.
  • Vegetables, grains, and other items that have protein content will be restricted.

3. Neutral Amino Acid Remedy

  • Neutral amino acid supplements are available in the form of tablets and powder. This supplement helps in blocking the absorption of phenylalanine.
  • The concerned doctor will prescribe this if needed. Do not try it on your own.
  • Nutrients and proteins required for the baby’s growth

4. PKU Medicines

  • Drug sapropterin is approved by FDA (Food & Drug Administration). This medicine works by increasing the body’s tolerance levels of phenylalanine.
  • This medicine is used along with the PKU diet. However, this medicine may not be prescribed to everyone by the health care provider.

5. PKU Formula for Toddlers and Babies

  • Breastmilk and regular infant formula contain high levels of phenylalanine. PKU babies need to have a phenylalanine-free formula.
  • Consult a dietician who can calculate and suggest the right proportion of breast milk or regular infant formula added to the phenylalanine-free formula.
  • Solid food that has low levels of phenylalanine can be given to PKU kids like infants.

Home Remedies to Manage a Baby With PKU

Having a baby with PKU needs to be managed well at home. Below are some simple and effective home remedies and methods that parents can try to manage a baby with PKU.


1. Maintain track, review, and measure

It is crucial to keep track and record every bit of food eaten every day by the baby. Sticking to the dietician’s diet plan and guidelines will go a long way in managing the treatment. Buy food measuring cups, measuring spoons, and a kitchen scale to measure the exact portion of food that needs to be given to the baby. The amount of phenylalanine consumed needs to be calculated every day.  Divide the portion of each snack and meal to consume food with normal PKU levels.

2. Buy food products that are low in protein

It is good to buy foods that are very low in protein content and readily available in retail food stores, such as low protein bread, flour, rice, pasta, etc. The best part is, these foods that PKU kids eat are similar to what everyone else eats. It brings a sense of togetherness to the family. These products like the PKU formula may not be very pocket-friendly but are worth trying if you have to maintain your expenses properly.

3. Experiment with food

Use your creative bent of mind to experiment with food. Consult your diet planner to add variety to your food, keeping in mind the PKU limitations. You can try different cooking methods and seasonings to cook vegetables and other food with low phenylalanine content. Measure and count all your ingredients to suit an individual’s diet plan.

How to Support a Child Living With PKU?

It is challenging to live with a PKU child. Below are some strategies that can be tried.


  • Keep yourself well informed Read about the facts on PKU wherever possible. Consult your dietician, treating doctor, pediatrician whenever you have questions about PKU.
  • Keep an open mind to earn from others’ experiences Use social media or online groups to post your queries, check if others are already dealing with PKU, and find out how they are coping since you can use their ideas.
  • Your registered dietitian who comes with experience in PKU can help you plan delicious low-phenylalanine meals. Take ideas for birthday and holiday meals.
  • Plan your diet when you intend to eat out. Going to a restaurant for a family meal is always fun. Check with the restaurant what kind of food they offer that meets the PKU requirements, otherwise get some home-cooked food for your kid.
  • It is always not about food  the overall mental, emotional and social well-being is equally important. Motivate your child to hone their hobby skills, music, sports, etc., and let them plan holiday festivals and traditions.
  • Allow your child to prepare their menu. Let them choose the vegetables, fruits, and cereals they want to eat, and older children can maintain their food tracker.
  • Plan your grocery shopping list keeping the family’s requirements in mind. Similarly, plan well in advance when you go for family picnics, road trips, and potluck parties. Knowing about the dietary restrictions to meet the PKU guidelines will always be helpful.

PKU is a lifelong condition. However, with some planning and the right guidance, you can overcome the challenges and make life easy for your PKU kid and yourself. Continuously research this topic and consult your doctor, dietitian in a scheduled & timely manner. Maintain the food trackers and perform routine PKU screening. All this put together will help your PKU child lead a healthy life. 

Also Read:


Age Wise Infant Checkup
Coombs Test in Baby
Hearing Tests for Newborn Infants

This post was last modified on November 25, 2021 6:11 pm

Recent Posts

List of Animals That Start With Q

Have you ever wondered about the fascinating world of animals whose names start with the…

December 6, 2023

List of Animals That Start With T

Welcome to a thrilling exploration of the animal kingdom, where we dive into the unique…

December 6, 2023

Rhyming Riddles For Kids To Boost Their Creativity

Welcome to the enchanting world of rhyming riddles – a magical place where words dance…

December 6, 2023

Mother’s Day Wishes, Quotes and Messages for Your Lovely Wife

Expressing your love and appreciation for your lovely wife on Mother's Day is a beautiful…

December 6, 2023

Essay On Golden Temple – 10 Lines, Short and Long Essay For Children and Students

An essay on the Golden Temple in English, tailored for school kids, serves as a…

December 6, 2023

Green Fruits With Their Types and Names for Kids

Welcome to the vibrant world of green fruits! This fascinating journey is specially designed for…

December 6, 2023