PREPARATION OF THE FIRST EUROPEAN WORKING STANDARD FOR PHENYLALANINE DETERMINATION IN DRIED BLOOD SPOTS

Objective-To develop a standard preparation for measurement of phenyla lanine in blood spots in phenylketonuria against which manufacturers o f kits for phenylalanine determination could calibrate their own blood spot calibrators. Methods-As most of the variation of phenylalanine c oncentration in dried blood spots is due to the way the blood spot cal ibrators are prepared, a minimum set of prerequisites for the preparat ion of blood spot calibrators was established by a group of scientific experts and manufacturers. A ((European working standard for phenylal anine in blood spots)) (EWS-Phe-01) was prepared and distributed to ma nufacturers taking part in this project. Results-The control of the ho mogeneity, linearity, and stability of the EWS-Phe-01 batch gave resul ts within expected ranges. The preliminary results of the recalibratio n of calibrators for phenylalanine against EWS-Phe-01 by the participa ting manufacturers were promising; the differences between measurement s were much decreased. Conclusion-Manufacturers have agreed to use EWS -Phe-01, and since November 1996 EWS-Phe calibrators have been routine ly available from these companies. This pilot study may act as a model for minimising discrepancies found in other screening tests.