An Evaluation of Routine Follow-up Blood Screening of Infants for Phenylketonuria

Abstract

ROUTINE follow-up blood testing has been advocated for newborn phenylketonuria screening programs.^{1 2 3} This advocacy derives from the fact that an occasional neonate with the disorder is undetected in routine screening programs that generally use a single blood specimen obtained during the first days of life⁴ and from the assumption that these infants would be detected if a second or follow-up blood specimen were obtained several weeks later. It is assumed that such affected neonates are not identified from the initial blood specimen because this specimen may be obtained before enough protein has been ingested to result in demonstrable hyperphenylalaninemia.¹ These . . .