Patient Noncompliance

Compliance is a challenge for PKU patients of all ages.⁴¹ There is evidence that even patients who receive appropriate treatment have difficulties with problem solving, abstract reasoning, and other executive functions.^36,42,43

Dietary compliance is low¹⁴
Diet management is restrictive
Diet management is burdensome
Diet management is misunderstood by patients
Noncompliance can be self-perpetuating

Dietary compliance is low¹⁴

• A study of patients at four PKU clinics indicated widespread noncompliance to dietary management standards.
• 30% of patients <10 years of age had blood Phe concentrations above the recommended level, while 80% of patients aged ≥15 years had blood Phe levels above the recommended threshold.

Percent of Patients With Phe Concentrations Above Target Range Increases With Age

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Diet management is restrictive

• The low-Phe diet is mainly composed of a satiating elemental liquid formula instead of natural foods.⁴⁴
• Low-protein specialty foods that complement the diet are far more expensive than regular foods.⁴¹
• The cost can be a significant burden.^41,45
  • The formula can be unpalatable.^41,44
• There is a significant lack of variety in both the protein substitute products and in the small range of natural products that are allowed on the diet.⁴⁶

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Diet management is burdensome

• Patients are required to continuously monitor their Phe intake.²⁷
  • Many patients carry scales for weighing all the food they eat.
  • They commit to memory the Phe content of all the food they commonly eat.
  • Patients must also consult specialty cookbooks, food lists indicating Phe content, or lists they have compiled themselves.
• Clinic visits and blood tests can be inconvenient for patients, particularly when these occur frequently and the patients do not live near a PKU clinic.⁴¹

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Diet management is misunderstood by patients

• Phe levels are tracked in a somewhat unreliable way.
  • Blood tests may occur as infrequently as once a year.
  • Patients might assume that Phe content is distributed evenly within a food. For example, one french fry might be considered to have only one exchange, despite the size of the french fry.
• Phe tolerance changes over time.
  • Phe tolerance increases somewhat with age.⁴⁷
  • Phe tolerance increases when the body requires more protein, such as during periods of high growth, activity, or illness.^47,48,73

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Noncompliance can be self-perpetuating

• It is difficult for patients to return to the diet after quitting.³⁵
• The temptation of biological protein along with the inconvenience of tracking Phe levels can make it difficult for patients to stay on the strict diet.⁴⁹

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