Follow-up Screening for Phenylketonuria

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Abstract
To the Editor: In the March 15 issue, Sepe et al.1 questioned the use of follow-up tests to detect cases of phenylketonuria (PKU) missed on initial screening. Their questioning should not go unchallenged since they have neglected relevant and broader aspects of the matter.Missed cases in newborn testing for PKU can arise for administrative, technical, biologic and statistical reasons. Of most immediate relevance to retesting post-neonatal infants for PKU is biologic variability, since testing before 72 hours of age will miss at least 10 per cent of infants with PKU.2 Also, administrative loopholes in a state with one of . . .