PKU is a rare metabolic disorder which prevents the normal breakdown and use of protein containing foods by the body. It is due to a deficiency of an enzyme (phenylalanine hydroxylase or PAH) which breaks down protein.

Protein is made up of amino acids. One of these amino acids is called phenylalanine and would normally be changed into another amino acid – tyrosine. However, in PKU because the enzyme is not very active, or is missing, the phenylalanine is unable to be converted into tyrosine and will accumulate in the blood. If left untreated the build-up of phenylalanine can damage the brain and cause severe learning difficulties. Fortunately, many countries have a newborn screening programme for PKU. This means that PKU is detected in the first few days of life and treatment can start as soon as diagnosis is confirmed.

What is a low phenylalanine diet?

A low phenylalanine diet is the main treatment for phenylketonuria (PKU). People with PKU must restrict phenylalanine which is found in protein. However, phenylalanine (protein) cannot be removed completely, so it is given in measured exchange amounts each day.

A low phenylalanine diet can be highly complex with foods recognised in various groups depending upon their phenylalanine content. Most food labels don’t specify phenylalanine so protein content is taken as a proxy and a calculation is done on the basis of protein level and food mass to ascertain the “exchange” value of the food.

Why were we engaged?

We were asked to design and build a digital application which could fulfill the following requirements:

  1. Bring to life the coding and labeling system used within a low phenylalanine diet.
  2. Create an easy look up guide for foods to enable patients and carers to know, which foods were safe and which need caution or should be avoided.
  3. Provide a tool which simplified the calculation process for “exchanges” within the low phenylalanine diet.

What we did

Find your audience

Working closely with the Birmingham Children’s Hospital (BCH) PKU team, we first ascertained the audience for the application. As PKU is often diagnosed at infant stage the users of the app would be parents, carers and wider family as well as patients themselves.

Build for everyone

As we needed to ensure that the application was as accessible as possible we decided that there should be a web browser base as well as native Android and IoS applications. This means that the app would be accessible and functioning both in online and offline mode and across the most number of devices, whether they were mobile, laptop or tablets.


We used a very collaborative approach to design with the BCH team, allowing multiple iterations. We also ran virtual focus groups with intended end users. This allowed the design to evolve and reflect a wide variety of feedback.

Build & Trials

The first iteration of the app has been built and deployed within controlled trials at the Birmingham Children’s Hospital. The trial groups are split into two, with one group using the digital application and the second group using the existing paper based methods. We provide the facilitation and onboarding process for all participants in the trial.

Further Development

Once the trials are over we will gather further feedback and analyse the usage data to add functionality and then there will be a full release to the public.