Enzymatic method for phenylketonuria screening using phenylalanine dehydrogenase

An enzymatic method using phenylalanine dehydrogenase (PheDH;EC 1.4.1.-) for the determination of phenylalanine in blood-spot specimens has been developed for the Cobas Bio centrifugal analyser. Method accuracy was established by correlation of results from blood spots with phenylalanine values obtained by quantitative aminoacid analysis on simultaneously collected plasma specimens. The phenylalanine dehydrogenase method demonstrated linearity to 2500 mumol/L and had recoveries of 89.4 +/- 4.6% (mean +/- SEM). The between-run precision using blood-spot specimens was 9.8% at 285 mumol/L. In the context of a routine newborn screening program, the enzymatic method was found to have a lower false-positive rate (1% vs 3%) when evaluated against the classical fluorimetric Autoanalyser method.