Phenylketonuria (PKU) Test

PKU (Phenylketonuria) Screening

Test Overview

A phenylketonuria (PKU) test is done to check whether a newborn baby has the enzyme needed to use phenylalanine in his or her 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 mental retardation.

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 now tested for PKU right after birth. About 1 in 12,000 babies have PKU.¹ In Canada, PKU occurs more in whites and First Nations (Aboriginal) peoples and is less common in blacks, Hispanics, and Asians. It is inherited from either the mother or father.

The blood sample for PKU is usually taken from your baby's heel (called a heel stick) 2 to 3 days after birth. A urine PKU test is done on a baby who did not have a blood test and who is older than 6 weeks.

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Author:	Carrie Henley Jan Nissl, RN, BS	Last Updated: May 26, 2006
Medical Review:	Michael J. Sexton, MD - Pediatrics Thomas Emmett Francoeur, MDCM, CSPQ, FRCPC - Pediatrics
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