Diagnosis

Newborn blood testing identifies almost all cases of phenylketonuria. All 50 states in the United States require newborns to be screened for PKU. Many other countries also routinely screen infants for PKU.

If you have PKU or a family history of it, your doctor may recommend screening tests before pregnancy or birth. It's possible to identify PKU carriers through a blood test.

Testing your baby after birth

A PKU test is done a day or two after your baby's birth. The test is done after your baby is 24 hours old and after your baby has ingested some protein in the diet to ensure accurate results.

  • A nurse or lab technician collects a few drops of blood from your baby's heel or the bend in your baby's arm.
  • A laboratory tests the blood sample for certain metabolic disorders, including PKU.
  • If you don't deliver your baby in a hospital or are discharged soon after the birth, you may need to schedule a newborn screening with your pediatrician or family doctor.

If this test indicates your baby may have PKU:

  • Your baby may have additional tests to confirm the diagnosis, including more blood tests and urine tests
  • You and your baby may have genetic testing to identify gene mutations

Treatment

The main treatment for PKU includes:

  • A lifetime diet with very limited intake of protein, because foods with protein contain phenylalanine
  • Taking a PKU formula — a special nutritional supplement — for life to make sure you get enough essential protein (without phenylalanine) and nutrients that are crucial for growth and general health

A safe amount of phenylalanine differs for each person with PKU and can vary over time. In general, the idea is to consume only the amount of phenylalanine that's necessary for normal growth and body processes, but no more. Your doctor can determine a safe amount through:

  • Regular review of diet records, growth charts and blood levels of phenylalanine
  • Frequent blood tests that monitor phenylalanine levels as they change over time, especially during childhood growth spurts and pregnancy
  • Other tests that assess growth, development and health

Your doctor may refer you to a registered dietitian who can help you learn about the PKU diet, make adjustments to your diet when needed, and offer suggestions on ways to manage PKU diet challenges.

Which foods to avoid

Because the amount of phenylalanine that a person with PKU can safely eat is so low, it's crucial to avoid all high-protein foods, such as:

  • Milk
  • Eggs
  • Cheese
  • Nuts
  • Soybeans
  • Beans
  • Chicken
  • Beef
  • Pork
  • Fish

Potatoes, grains and other vegetables that have protein will likely be limited.

Children and adults also need to avoid certain other foods and beverages, including many diet sodas and other drinks that contain aspartame (NutraSweet, Equal). Aspartame is an artificial sweetener made with phenylalanine.

Some medications may contain aspartame and some vitamins or other supplements may contain amino acids or skim milk powder. Check with your pharmacist about the contents of over-the-counter products or prescription medications.

Talk with your doctor or registered dietitian to learn more about your specific dietary needs.

Formula for people with PKU

Because of the restricted diet, people with PKU need to get essential nutrients through a special nutritional supplement. The phenylalanine-free formula provides protein and other essential nutrients in a form that's safe for people with PKU.

Your doctor and dietitian can help you find the right type of formula.

  • Formula for babies and toddlers. Because regular infant formula and breast milk contain phenylalanine, babies with PKU instead need to consume a phenylalanine-free infant formula. A dietitian can carefully calculate the amount of breast milk or regular formula to be added to the phenylalanine-free formula. Parents introduce solid foods with low levels of phenylalanine to children with PKU on the same schedule used for other infants.
  • Formula for older children and adults. Older children and adults continue to drink or eat a protein substitute formula daily, as directed by a doctor or dietitian. Your daily dose of formula is divided between your meals and snacks, instead of consumed all at once. The formula for older children and adults is not the same as the one used for infants, but it works on the same principle. It provides essential protein (amino acids) without phenylalanine and is continued for life.

The need for a nutritional supplement, especially if your child doesn't find it appealing, and the limited food choices can make the PKU diet challenging. But families need to make a firm commitment to this lifestyle change because it's the only way to prevent the serious health problems that people with PKU can develop.

Neutral amino acid therapy

Another possible addition to the PKU diet is a supplement called neutral amino acid therapy in powder or tablet form. This supplement may block some absorption of phenylalanine. This may be a treatment option for adults with PKU. Ask your doctor or dietitian if this supplement is appropriate for your diet.

PKU medication

The Food and Drug Administration (FDA) has approved the drug sapropterin (Kuvan) for the treatment of PKU. It works by increasing your tolerance to phenylalanine. The drug is for use in combination with a PKU diet. But it doesn't work for everyone with PKU.

In approving sapropterin, the FDA directed that studies continue because there are no long-term studies on the drug's efficacy and long-term safety.

Lifestyle and home remedies

Some strategies to help manage PKU may include the following.

Keep track and measure correctly

If you or your child is following a low-phenylalanine diet, you'll need to keep records of the food eaten every day to be sure you're sticking to the specific, individualized dietary guidelines recommended by your dietitian.

To be as accurate as possible, measure food portions using standard measuring cups and spoons and a kitchen scale that reads in grams. The food amounts are compared with a food list or are used to calculate the amount of phenylalanine eaten every day. Each meal and snack includes the appropriately divided portion of your daily PKU formula.

Food diaries or computer programs are available that list the amount of phenylalanine in baby foods, solid foods, PKU formulas, and common baking and cooking ingredients.

Buy low-protein products

To add variety to your diet, buy some of the many low-protein products, such as low-protein pasta, rice, flour and bread, which are available through specialty food retailers.

These products allow people with PKU to eat some meals that more closely resemble what everyone else is eating. Like the PKU formulas, these products can be expensive, but you might consider splurging on a few favorites with the money you save on dairy and meat products.

Be creative

Talk with your dietitian to find out how you can be creative with foods to help you stay on track. For example, use seasonings and a variety of cooking methods to transform lower phenylalanine vegetables into a whole menu of different dishes. Herbs and flavorings low in phenylalanine can pack a flavorful punch. Just remember to measure and count every ingredient and adjust recipes to your individualized diet.

If you have any other health conditions, you may also need to consider those when you plan your diet. Talk with your doctor or dietitian if you have any questions.

Coping and support

Living with PKU can be challenging. These strategies may help:

  • Stay informed. Knowing the facts about PKU can help you take charge of the situation. Discuss any questions with your pediatrician, family doctor, geneticist or dietitian. Read books and cookbooks specifically written for people with PKU.
  • Learn from other families. Ask your doctor about local or online support groups for people dealing with PKU. Talking with others who have mastered similar challenges can be very helpful. The National PKU Alliance is an online support group for adults with PKU.
  • Get help with menu planning. A registered dietitian with experience in PKU can help you devise delicious low-phenylalanine dinners. He or she may also have great ideas for holiday meals and birthdays.
  • Plan ahead when you eat out. A meal at the local restaurant gives you a break from the kitchen and can be fun for the whole family. Most places offer something that fits into the PKU diet. But you may want to call ahead and ask about the menu or bring food from home.
  • Find sources of financial aid. Ask your doctor or dietitian if there are programs or insurance plans that help cover the high costs of formula and low-protein foods. Also, see if your local school lunch program will accommodate special dietary needs.
  • Don't focus on food. Encourage children with PKU to focus on sports, music or favorite hobbies, not on just what they can and can't eat. Also consider creating holiday traditions that center on special projects and activities, not just food.
  • Let your child help manage his or her diet as early as possible. Toddlers can make choices about which cereal, fruit or vegetable they'd like to eat and help measure out portions. They can also help themselves to pre-measured snacks. Older children can help with menu planning, pack their own lunches and keep their own food records.
  • Make your grocery list and meals with the whole family in mind. A cupboard full of restricted foods can be tempting to a child or adult with PKU, so try to focus on foods that everyone can eat. Serve stir-fried vegetables that are lower in protein. If the other family members wish, they can add peas, corn, meat and rice. Or set up a salad bar with low-protein and moderate-protein options. You can also serve the whole family a delicious low-phenylalanine soup or curry.
  • Be prepared for potlucks, picnics and car trips. Plan ahead, so there's always a PKU-friendly food option. Pack dehydrated fruit snacks, raisins and lower protein crackers for the car. Take fruit kebabs or vegetable skewers to a cookout, and make a low-phenylalanine salad for the neighborhood potluck. Other parents, friends and family members will likely be accommodating and helpful if you explain the dietary restrictions.
  • Talk to teachers and other staff in your child's school. Your child's teachers and cafeteria staff can be a big help with the PKU diet if you take the time to explain its importance and how it works. By working with your child's teachers, you can also plan ahead for special school events and parties so that your child always has a treat to eat.
  • Maintain a positive food attitude. When children know nothing but the foods they are given, they can be surprisingly accepting of the PKU diet — especially when their parents are positive problem-solvers.

Preparing for your appointment

Phenylketonuria is generally diagnosed through newborn screening. Once your child is diagnosed with PKU, you'll likely be referred to a medical center or specialty clinic with a doctor who specializes in treating PKU and a dietitian with expertise in the PKU diet.

Here's some information to help you get ready for your appointment and know what to expect from your doctor.

What you can do

Before your appointment:

  • Ask a family member or friend to come with you — sometimes it can be difficult to remember all of the information provided during an appointment.
  • Make a list of questions to ask your doctor and dietitian to help you make the most of your time together.

Some basic questions to ask may include:

  • How did my child get PKU?
  • How can we manage PKU?
  • Are there any medications to treat this disease?
  • What foods are completely off-limits?
  • What is the recommended diet?
  • Will my child have to stay on this special diet for life?
  • What kind of formula will my child need? Can my child have breastmilk?
  • Are there any other supplements needed?
  • What happens if my child eats a food that he or she is not supposed to eat?
  • If I have another child, will he or she have PKU?
  • Are there brochures or other printed material that I can have? What websites do you recommend?

What to expect from your doctor

Your doctor is likely to ask you several questions. Be ready to answer them to reserve time to go over points you want to focus on. For example, your doctor may ask:

  • Has your child had any symptoms that concern you?
  • Do you have any questions about your child's diet?
  • Are you having any difficulty following the diet?
  • Has the growth and development of your child been typical of other children the same age?
  • Have you ever had genetic testing?
  • Do any other relatives have PKU?
Jan. 27, 2018
References
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  3. Learning about phenylketonuria (PKU). National Human Genome Research Institute. https://www.genome.gov/25020037/learning-about-phenylketonuria/. Accessed Oct. 8, 2017.
  4. Phenylketonuria (PKU). Merck Manual Professional Version. http://www.merckmanuals.com/professional/pediatrics/inherited-disorders-of-metabolism/phenylketonuria-pku. Accessed Oct. 8, 2017.
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