The Effect of Phenylalanine Test Frequency on Management of Phenylketonuria (PKU)

Objectives: The analysis was undertaken to investigate the extent to which the frequency of blood tests is associated with control of phenylalanine (Phe) levels among children with phenylketonuria (PKU). Methods: Multivariate and age-stratified regression analyses were run on Phe test results (N=3,015) from sixty-two sample subjects, aged eight years or younger, treated in four PKU clinics in the intermountain West over the period 1980 to 1995. More detailed regressions were run on the subset of observations (N=1,965) from the thirty-three subjects treated in the Utah clinic. Results: Each additional week of delay between tests was associated with a 10% reduction (95% CI=0.83-0.98) in the likelihood that a subsequent Phe reading would fall below the recommended upper limit of the recommended range (#6mg/dl). The relationship was most pronounced among sample subjects three years and older (0.86, 95% CI=0.73-1.01) and in the analysis of Utah clinic subjects, which included additional sociodemographic controls (0.83, 95% CI=0.75-0.92). Conclusions: Since the advent of universal screening for PKU nearly forty years ago, the challenge faced by patients and families as well as by health professionals, has been to improve the daily management of the condition. The significant relationship between Phe test frequency and Phe levels reported in this analysis suggest that opportunities for improvement in the management of PKU may reside with institutional and technological changes in the administration and utilization of the Phe test.