Abstract
Phenylketonuria screening by blood phenylalanine assay has been carried out on 41 821 newborn infants using the bacteriological inhibition assay method and 22 365 of the samples were tested also by an automated fluorimetric technique. The methods were equally effective in detecting infants with phenylketonuria and false positives can be kept to small numbers in both cases without risk of missing true positive results. A large proportion of infants having borderline results, particularly with the fluorimetric method were shown to have transient tyrosinaemia. Since the cost of the fluorimetric method compared favourably with the bacteriological assay and it has some practical advantages, it should be considered seriously for phenylketonuria mass screening.