I have been working as a dietitian for 16 years and for the last 10 years I have been specialising in the area of Inherited Metabolic Disorders (IMD) of which Phenylketonuria (PKU) is a major part of my caseload.
Back in 2008 I was employed as the first dietitian for adults with IMD in the West Midlands to help set up the adult services. This was needed as adults with IMDs were living longer into adulthood. Screening for PKU started in the late 1960s so we now have adults in their late 40s with early treated PKU (screened and started treatment straight away) and adults over 50 with late treated PKU (treatment started after diagnosis).
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?
"First of all, when someone needs a specialist diet - don't panic"
First of all when someone needs a specialist diet – don’t panic! At this point in time the best source of information is the patient or their family. Be honest and let them know that it is not your area of expertise so you need their help.
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.
Don’t be surprised if you find a person with PKU who is not on the low phenylalanine diet. There are still older people with PKU out there that have been lost to follow up or that came off their low phenylalanine diet in their teenage years.
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.
If the individual follows a low phenylalanine diet then check which center they are under so that you can call their metabolic dietitian for advice. Find out how strictly they follow their diet – are they only on 5 or 10 exchanges (grams of protein) per day or do they not bother counting the protein anymore.
"They should be taking a protein substitute which is a prescription item"
They should be taking a protein substitute which is a prescription item so you may need to organize a supply through the hospital or if they are only in for a few days they may bring them from home. They are either liquids or powders made into drinks taken 3-4 times a day or lots of tablets (at least 80 per day for adults!).
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 the patient needs a tube feed then first of all find out how strictly they follow the low phenylalanine diet and how long they are going to need the feed for. If it is a patient who does not follow a low phenylalanine diet then they can have a normal tube feed.
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
If the patient is catabolic due to illness or injury then their phenylalanine concentrations may be higher than usual, so there is no point in testing them as they will be high from catabolism rather than protein intake. If the patient is pregnant then they must keep their phenylalanine concentrations between 120-360umol/l to keep the baby safe 1 so they must monitor their phenylalanine concentrations 2-3 times a week.
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.