Kids Home > Newborn PKU Screening

Shortly after birth, your child will likely be screened for a genetic disorder called phenylketonuria (PKU). Newborn PKU screening is done with a blood test. A healthcare provider will collect the blood from the baby's heel or from a vein. In many cases, a newborn will be screened twice -- once soon after birth, and once a few days later.

What Is Newborn PKU Screening?

PKU stands for phenylketonuria. It is a genetic disorder that causes problems with an important enzyme known as phenylalanine hydroxylase. This enzyme is responsible for breaking down the naturally occurring amino acid phenylalanine, which is found in most foods that contain protein. You might hear it said that people with PKU are missing the enzyme, which is only partially true. In people with PKU, a mutation in a specific gene causes the enzyme to be nonfunctional.
 
Why does this matter? If PKU is undetected and untreated, it eventually causes severe mental retardation. Because the symptoms develop gradually, parents and doctors might not even notice problems until it is too late and the damage has been done. PKU can be treated by adhering to a special diet, which for babies means using a special formula, not breast milk or regular formula. Although PKU is rare, it is worthwhile to screen all babies for this condition shortly after birth to help prevent the devastating effects of the untreated disease.
 

How Is the PKU Test Done?

The PKU screening test is a blood test. The blood can be collected from the heel of the baby (a lancet is used to poke a small hole in the skin; then the blood is dotted onto special collection cards). Alternatively, a regular "blood draw" using a vein can also be used. In fact, one study suggests that a regular blood draw is faster and less painful than a heel stick for newborn PKU tests.
 
In most states, law requires that all babies be screened for other diseases too as part of a newborn screening program, not just PKU, so you might hear your doctor or nurse refer to it as a "newborn screening" test instead.
 
The exact timing and the number of PKU tests required will vary, depending on your hospital, the type of PKU test the lab uses, and state laws.
 
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
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