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
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,
It is important to find this disease
early. All babies in the United States and Canada are tested for PKU right after birth. PKU
occurs more in whites and Native Americans and is less common in blacks,
Hispanics, and Asians. To have the disease, you must inherit the
gene from each parent. The
United States Preventive Services Task Force
recommends that all newborns be tested for PKU.1
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. A follow-up test is usually done
at age 7 to 10 days. A urine PKU test is done on a baby who did not have a
blood test and who is older than 6 weeks.
Why It Is Done
A phenylketonuria (PKU) test is done to
see whether a newborn baby has the enzyme needed to use
phenylalanine in his or her body.
important to test your baby for PKU soon after birth to prevent brain damage.
Phenylalanine blood levels in a baby with PKU start to rise within 24 hours of
drinking breast milk or formula. A PKU test done 2 to 3 days after birth will
show whether your baby has PKU.
How To Prepare
Your baby should be drinking breast
milk or formula for 24 hours before the blood sample is taken. PKU test results
are more likely to be correct if the blood sample is taken after the baby has
been drinking milk or formula for at least 48 hours.
If your baby
is older than 6 weeks, he or she may have a PKU urine test. You do not need to
do anything before your baby has this test.
How It Is Done
Your baby's heel is cleaned with
alcohol and then the heel is poked with a small needle. Several drops of blood
are collected inside circles on a special piece of paper. When enough blood has
been collected, a small bandage is put on the site.
For a urine
test, a drop of special fluid or a special test strip is put on a diaper with