Phenylketonuria (PKU) Screening

A PKU screening test measures the amount of a protein called phenylalanine (Phe) in a sample of a newborn's blood. Phe is in all foods that contain protein such as milk, meats, and nuts. It's also in an artificial sweetener called aspartame.

If a newborn has high levels of Phe in their blood, it could mean that they have phenylketonuria (PKU). PKU is a rare genetic disorder, meaning it's caused by changes (also called variants or mutations) in a gene. Genes are parts of DNA in your cells that you inherit from your parents.

You inherit two copies of each gene, one from each parent. Genes carry information that controls what you look like and how your body works. The gene involved in PKU helps make a substance that breaks down part of Phe in food.

So, a change in that gene can make it harder for your body to break Phe down. This means that if you have PKU and eat foods with Phe, the Phe will build up in your blood. High levels of Phe can permanently damage your nervous system and brain, leading to various health problems such as seizures and possibly learning disabilities.

PKU can vary from mild to severe, depending on whether the changed gene still works somewhat or has stopped working completely.

How to prepare

There are no special preparations needed for a PKU test.

Sample type

Blood

Other names for this test

PKU newborn screening, PKU test