Screening Newborn Infants for Phenylketonuria

Abstract

Using a quantitative method to determine serum phenylalanine that requires 25μl of serum from capillary blood, 4,000 newborn infants were tested for phenylketonuria. The mean and standard deviation for this sample are 2.09 ± 0.51 mg/ 100 ml. The values are not appreciably influenced by maternal age, gravida, sex, race, birth weight, or age of the infant. The lowest recorded serum phenylalanine on a phenylketonuric infant is about seven standard deviations above the mean for the normal newborn population. In this survey, only eight of the 4,000 infants (0.2%) temporarily showed serum phenylalanine levels above 4.0 mg/100 ml. Extrinsic factors, such as high tyrosine levels or heterozygosis, could account for this increase. This method appears to combine a high probability of detecting affected infants with a small frequency of false positives.