Phenylketonuria (PKU): summary
Updated 4 April 2025
Applies to England
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In this information, the word 鈥榳e鈥� refers to the NHS service that provides screening.
This information is for parents if their baby is suspected of having PKU or has been diagnosed with PKU following their newborn blood spot screening test (鈥榟eel prick test鈥�). It will help you and your health professionals to talk through the next stages of your baby鈥檚 care.
About PKU
Phenylketonuria (pronounced as fee-nile-key-tone-you-ree-ah), or PKU, is a rare but treatable inherited metabolic disorder that prevents the normal breakdown of protein. Babies with PKU inherit 2 faulty copies of the gene for PKU, one from each parent.
Untreated PKU can lead to long-term health problems, including severe learning difficulties and behavioural problems, but with newborn screening and early treatment this can be prevented.
Screening and diagnosis of PKU
Newborn blood spot (鈥榟eel prick test鈥�)
When your baby was about 5 days old, your midwife took some blood from your baby鈥檚 heel for their newborn blood spot screening test (the 鈥榟eel prick test鈥�). The newborn blood spot screening test measures the amount of some amino acids in the blood. A high level of the amino acid phenylalanine suggests your baby may have PKU. This is called a screen positive result.
Diagnostic tests
If your baby has a screen positive result, you will be seen by a metabolic doctor, dietitian and nurse specialist (the 鈥榤etabolic team鈥�). The team will provide advice and support. Blood tests will be carried out to confirm if your baby has PKU.
You will need to wait a few days for the test results to be reported. During this time, you can continue to breastfeed or give normal infant formula.
Treatment
If your baby does have PKU, the metabolic team will explain the condition in more detail and answer any questions you might have. They will start your baby on a special diet (to restrict phenylalanine intake), and they will arrange regular follow-up appointments. Following the diet is very important for your baby鈥檚 health.
Confidentiality
The NHS screening programmes use personal information from your NHS records to invite you for screening at the right time and to ensure you receive high quality care and to improve the screening programmes. Find out more about how your information is used and protected, and your options.
More information and support
The metabolic team will be happy to discuss any queries you may have.
For more information, see Phenylketonuria (PKU): further information.
Further information can be found at . The Metabolic Support UK team can be contacted at:
- Phone: 0845 241 2173 or 0800 652 3181
- Email: [email protected]
The also provides information and support. The NSPKU team can be contacted on:
- Phone: 030 3040 1090
- Email: [email protected]
The British Inherited Metabolic Diseases Group (BIMDG) website has a .
NHS.UK has and .