PHENYLKETONURIA SCREENING WITH A FLUOROMETRIC MICROPLATE ASSAY

A fluorometric assay in microtitre plates for the screening of phenylk etonuria was evaluated and adapted to a neonatal screening programme. Using this assay, it is possible to determine quantitatively the pheny lalanine concentration in dried blood spots on filter paper. The test exhibited a linear calibration curve with a good slope as well as suff icient precision and accuracy in the statistical analysis. Interferenc e by other amino acids and antibiotics was not observed. Only elevated concentrations of leucine interfered to a small degree. The phenylala nine concentration in dried blood spots of 13 phenylketonuria patients correlated to that in serum. 7381 dried blood samples of newborn infa nts were tested simultaneously by both the fluorometric and the Guthri e test. The results did not show significant differences. We screened 29182 newborns using the fluorometric assay and an online data process ing programme. The internal repetition rate was 0.64%, the external re call rate 0.15%. False negative results were not observed. In December 1991 the fluorometric method replaced the Guthrie test in our routine programme for phenylketonuria screening, and was introduced as a foll ow up test for phenylketonuria patients.