Phenylketonuria (PKU) Screening

Phenylketonuria (PKU) Screening

Phenylketonuria, or PKU, is an inherited disorder that can be detected through screening. It results from the inability of the body to metabolize the amino acid phenylalanine, leading to abnormal amounts of phenylalanine in the blood. PKU is a serious condition that can cause irreversible intellectual disability and seizures, so it is important to diagnose it as early as possible.


No preparation is typically necessary for a PKU screening. It is done as a simple blood test from a heel prick and heel stick. The blood is then sent to a laboratory to be analyzed for levels of phenylalanine. A PKU screening should not be done if the infant is ill or feverish, as those conditions can interfere with the screening results.


The procedure for a PKU screening is simple. A small sample of blood is taken from the heel of the baby. The heel will first be cleaned with an alcohol swab and then pricked with a needle to draw a few drops of blood. The blood is then placed on an absorbent card and sent to a laboratory for testing. The results usually take a few days to come back.

Types of PKU Screens

The type of screen performed on an infant will vary depending on the state or country where the baby is born. In the United States, the most common test is the Guthrie test, which measures the levels of both phenylalanine and other substances related to PKU in the blood. Other types of PKU screenings are also available, including the tandem mass spectrometry (TMS) test and the enzyme-linked immunosorbent assay (ELISA) test.

Risks and Benefits

The risks associated with a PKU screening are extremely limited. The heel prick itself may cause slight discomfort, but it is usually over quickly. The test is also relatively inexpensive, since it can be performed rapidly and the results returned quickly.

The primary benefit of a PKU screening is the early detection of the condition. Early detection means that affected babies can begin treatment right away and that professionals can begin helping families understand and manage the condition. Without a screening, PKU could go undetected and the child may not receive the necessary treatment.

Why and When to Screen

Most babies in the US are tested for PKU shortly after birth. In some states, the testing is done before the baby leaves the hospital, while in other states the screening takes place a few days after the baby has gone home. The PKU screening is usually done between 24 and 72 hours after birth.

Screening for PKU is recommended for all babies in the US due to the known health risks associated with the disorder. PKU can cause severe mental retardation, seizures, and other problems, so it is important to identify babies with the condition as early as possible in order to begin appropriate treatment.