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Clinical Chemistry 47: 751-753, 2001;
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(Clinical Chemistry. 2001;47:751-753.)
© 2001 American Association for Clinical Chemistry, Inc.

Technical Briefs

Effect of Storage on Phenylalanine and Tyrosine Measurements in Whole-Blood Samples

Martin Beck1, Arend Bökenkampa, Nicolas Liappis1 and Michael J. Lentze1

1 The Children’s Hospital, Medical Center of Bonn University, D-53113 Bonn, Germany
a address correspondence to this author at: Universitätskinderklinik Bonn, Adenauerallee 119, D-53113 Bonn, Germany; fax 49-228-287-3444, e-mail a.boekenkamp@uni-bonn.de

With an incidence of 1 in 6600 newborns, phenylketonuria (PKU) is among the most common inborn errors of metabolism. PKU is caused by a deficiency of hepatic phenylalanine hydroxylase (1). The increase in the blood Phe concentration leads to permanent structural damage of the central nervous system as a result of disturbed myelination and neurotransmitter deficiency (2). If plasma Phe concentrations are normalized by a low-protein diet with supplementation of essential amino acids before 3 weeks of age, irreversible mental retardation is prevented (2). Still, strict metabolic control is mandatory throughout childhood (2) and perhaps into adult life (3). This is achieved by regular measurement of blood Phe and Tyr concentrations. Tyr is monitored because Phe hydroxylase deficiency renders it an essential amino acid in PKU. Recommendations for the duration and intensity of dietary control are not uniform (2); likewise, there is some variation in the local practices of PKU monitoring. The current guidelines of the German "Arbeitsgemeinschaft für Pädiatrische Stoffwechselerkrankungen" (The German Working Group for Metabolic Diseases) set a target range for Phe concentrations of 40–250 µmol/L, at least until age 10 (<=900 µmol/L is acceptable during adolescence) (4). These recommendations were based on data from samples that were analyzed immediately after sampling (Udo Wendel, University Children’s Hospital, Düsseldorf, Germany, personal communication). Pregnant women with even mild hyperphenylalaninemia also require strict dietary control of Phe concentrations to prevent PKU-induced fetopathy (1).

To ensure optimal . . . [Full Text of this Article]


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Copyright © 2001 by the American Association for Clinical Chemistry.