How practical are recommendations for dietary control in phenylketonuria?

In patients with phenylketonuria, blood phenylalanine concentration during childhood is the major determinant of cognitive outcome. Guidelines provide age-related recommendations for treatment. To ascertain the extent to which these aims are achievable, we audited results from four centres for the years 1994-2000. The median proportion of samples with phenylalanine concentrations above those recommended was less than 30% for those younger than age 10 years but almost 80% for those aged 15 years and older. Similarly, the median frequency of blood sampling, expressed as a proportion of that recommended, was more than 80% for patients younger than 10 years but less than 50% by age 15 years. Our results indicate the difficulty of maintaining control in phenylketonuria, especially in older rather than younger children.