The development of nonweighed pilot methods for estimating phenylalanine exchanges in non-phenylketonuria volunteers

Background: In children with phenylketonuria (PKU), the daily weighing of the phenylalanine allowance from food is advocated. There is a need to develop nonweighed methods of measuring dietary phenylalanine, aiming to ease caregiver burden and possibly improve dietary adherence. The accuracy of three methods (household measures, digital photographs and weighing) for measuring 50-mg phenylalanine exchanges for PKU was investigated in a randomised, controlled trial. Methods: There were 51 volunteers (32 females; 19 males; median age: 34 years, range 13-77 years), who were all unconnected with PKU. For three consecutive days, all volunteers attended a research centre and, each day, were randomly allocated a different method (household measures, digital photographs and weighing) for phenylalanine exchange measurement. On each day, they measured the amount of food equivalent to one 50-mg phenylalanine exchange for 24 common foods. All phenylalanine exchange samples (3672 samples) were then reweighed by the investigators. Results: No method of measuring 50-mg phenylalanine exchanges was accurate when used by volunteers. The median percentages (range) of all food samples within 10% of target were only 67% (41-98), 44% (4-96) and 41% (4-98) for weighing, household measures and photographs, respectively. The respective median (range) of samples within 20% of the target weights were: 96% (51-100) weighing, 82% (10-100) photographs and 80% (6-100) household measures. No noteworthy difference in accuracy was observed between household measures and photographs. Conclusions: Volunteers not associated with PKU could not measure 50-mg phenylalanine exchanges accurately using weighing, household measurements or photographs. Therefore, it is important to consider developing methods for improving accuracy of measurement of 50-mg phenylalanine exchanges in PKU.