PKU is a lifelong condition that is treated by a low phenylalanine (phe) diet managed mainly in specialist centres. As these specialist centres are in big cities, the patients are expected to travel into the centres to be seen. This means there are people with PKU who will be accessing other local health services or admitted into local hospitals that do not have any metabolic services.
If you come across someone with PKU in your clinic or on your ward you may have some questions. Is everyone with PKU on a strict low phenylalanine diet? Do you have to organise the special low phenylalanine diet while they are in hospital? If they need tube feeding do they need a low phenylalanine tube feed?
Ask them what type of diet they follow and how long they have been following it? Do they know what their recent phenylalanine concentrations have been? The recent European guidelines suggest phenylalanine concentrations in adults should be less than 600umol/l 1.
In this situation, it is safe for them to continue on their usual diet as the hospital is not the best place to initiate a complicated low phenylalanine diet! If they have been lost to follow up then suggest that they contact their GP about being referred to a specialist PKU center. You can reassure them that they won’t necessarily be made to restart a low phenylalanine diet, but they do need annual monitoring for any nutritional deficiencies or any PKU related symptoms.
Look through the hospital menu with them to see what they can choose as they cannot have any high protein foods. They will mainly only be able to choose vegetables, potato or rice. If they have mild PKU or they have a relaxed diet they may be able to choose pasta or bread. If they are on a strict diet, for example, if they are pregnant, then they will need specially manufactured low protein bread and pasta.
Discuss with your diet kitchen what special low protein meals they can prepare e.g. low protein pasta with a tomato sauce or a vegetable stew or curry with a measured amount of rice. The patient can either bring in the low protein products or you will have to order via your dietetic /catering ordering system.
If they are an adult on a relaxed diet and the tube feed is only needed for a couple of days then they could also have a normal tube feed. If they need to be on a strict low phenylalanine diet (e.g. they are pregnant), they are going to be on the tube feed long term or they wish to continue their low phenylalanine diet then you would have to organise a modular feed.
At this point definitely contact the patient’s metabolic dietitian or a local metabolic dietitian for help! The feed would include a liquid or powder protein substitute (at least 60g protein equivalent) that will have to be bolused down the tube over the day plus a protein free feed to top up the calorie, vitamin and mineral requirements such as Basecal200® (Vitaflo) which is a powdered feed that needs to be made up with water.
You will also need a small amount of protein, the amount will depend on the patient’s phenylalanine tolerance – for this you could use a liquid nutritionally complete supplement (e.g. Fortisip, Ensure, Fresubin, Aymes) and bolus in 3-4 times a day or mix with the protein free feed.
For example, to provide ~2000kcals 70g protein equivalent (including 10 exchanges of phenylanine / 10 g natural protein) per day
- PKU express® 20 x 3 per day (60g protein equivalent, phenylalanine free, 300kcals)
- Basecal200® x 7 sachets(1400kcals, 1400mls)
- Fortisip bottle 160mls (10g protein, 250kcals)
This is usually done using dried blood spot cards which your local metabolic dietitian can organise for you. If you are using a tube feed it is worth testing phenylalanine concentrations to check you have the phenylalanine content of the feed correct.
In conclusion, encountering someone with PKU outside of a metabolic clinic is quite rare, but knowing what to do is important. Remember the patient will be your main lead regarding their diet and the metabolic dietitian is only a phone call away!
1. van Wegberg, A.M.J., et al., The complete European guidelines on phenylketonuria: diagnosis and treatment. Orphanet Journal of Rare Diseases, 2017. 12(1): p. 162.