Phenylketonuria (PKU) Test
How It Feels
Your baby may feel a sting or a pinch
with a heel stick.
Usually, there are no problems from a heel
stick. A small bruise may develop.
phenylketonuria (PKU) test is done to check whether a
new baby has the
enzyme needed to use phenylalanine in his or her body.
If the heel stick screening test shows high phenylalanine levels,
a blood sample is taken from your baby's vein to confirm whether he or she has
What Affects the Test
Reasons the results may not be helpful include:
- Your baby was born early (premature). A baby
who weighs less than
5 lb (2.3 kg) may have high
levels of phenylalanine but not have phenylketonuria (PKU).
baby has been drinking milk for less than 24 hours. Best results occur after
your baby has been breast-feeding or drinking formula for 2 full
- Your baby is vomiting or refusing to eat. If the PKU test is
done before your baby has eaten for 2 days, the results may not be
- Your baby is getting