Neonatal screening for phenylketonuria: evaluation of an automated enzymatic method.

An enzymatic assay for phenylalanine using phenylalanine dehydrogenase is available in kit form (Quantase) for use with dried blood spot specimens and microtitre plates. The method has been automated by use of a sample processor and its performance and suitability for neonatal screening for phenylketonuria has been evaluated by comparison with the Guthrie bacteriological inhibition assay. The enzymatic method performed well with regard to precision and accuracy. It was able to differentiate between normal and raised phenylalanine concentrations for the purpose of screening, thus greatly reducing the repeat rate for equivocal results. There were, however, some concerns about its robustness for screening and its detection limit. The Quantase assay has the potential to be used as a large-scale routine neonatal screening method, if its use can be shown to be cost-effective.