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Phenylketonuria (PKU) Test

British Columbia Specific Information

​In British Columbia, prenatal screening is offered free of charge as a choice to all pregnant women with MSP coverage in BC. During your pregnancy, your health care provider will offer prenatal screening. Prenatal genetic screening can tell a pregnant woman her chance of having a baby with Down syndrome, trisomy 18, or an open neural tube defect.The tests can consist of one or more blood tests and ultrasound. These tests are ordered by your health care provider and can be done at any hospital or laboratory. For more information on prenatal genetic screening, visit BC Women's Hospital & Health Centre – Prenatal Screening and Perinatal Services BC - Prenatal Genetic Screening Program.

Every newborn baby born in BC and Yukon qualifies for screening. During the first few days after birth, your baby will have a newborn blood spot card screening test, which includes a blood test and examination by a doctor or midwife. Early detection and treatment of some disorders can help prevent disability and promote healthy development. For more information on newborn screening, visit

Test Overview

A phenylketonuria (PKU) test is done to check whether a newborn baby has the enzyme needed to use phenylalanine in their body. Phenylalanine is an amino acid that is needed for normal growth and development. If a baby's body does not have the enzyme that changes phenylalanine into another amino acid called tyrosine, the phenylalanine level builds up in the baby's blood and can cause brain damage, seizures, and intellectual disability.

The damage caused by PKU can begin weeks after the baby has started drinking breast milk or formula. Babies with PKU need foods low in phenylalanine to prevent severe brain damage. Phenylalanine is found in most foods that have protein, such as milk, cheese, and meats.

It is important to find this disease early. All babies in Canada are tested for PKU right after birth. To have the disease, you must inherit the gene from each parent.

The blood sample for PKU is usually taken from your baby's heel (called a heel stick). The test is done in the first few days after birth, as early as 24 hours after birth. The test may be repeated within the first week or two after birth.

Why It Is Done

A phenylketonuria (PKU) screening test is done to see whether a newborn baby has the enzyme needed to use phenylalanine in their body. If this test shows that your baby has a phenylalanine problem, the doctor will do further testing to check whether your baby has PKU.

It's important for your baby to have this screening test soon after birth. If a baby has PKU and treatment starts right away, problems (such as brain damage) are less likely to occur.

How To Prepare

You do not need to do anything before your baby has this test.

How It Is Done

A heel stick is used to get a blood sample from a baby. The baby's heel is poked, and several drops of blood are collected. Your baby may have a tiny bruise where the heel was poked.

How It Feels

A brief pain, like a sting or a pinch, is usually felt when the lancet punctures the skin. Your baby may feel a little discomfort with the skin puncture.

Risks

There is very little risk of a problem from a heel stick. Your baby may get a small bruise at the puncture site.

Results

If the heel stick screening test shows high phenylalanine levels, a blood sample is taken from your baby's vein. This is to confirm if your child has PKU.

Credits

Current as of: March 1, 2023

Author: Healthwise Staff
Medical Review:
John Pope MD - Pediatrics
Kathleen Romito MD - Family Medicine