Phenylketonuria screening in Moscow using a microplate fluorometric method

Abstract

We are reporting our experience in screening 139,664 newborn infants for phenylketonuria (PKU) in Moscow over a 16-month period, using a filter-paper blood microplate-based fluorometric method with a semiautomated fluorometer and computer control. We obtained the distribution of phenylalanine levels and we calculated the range of normal values in this newborn population. Quality control for this assay system was provided by a specially designed computer program and included computation of the mean for all normal values each day. These daily means were stored by 62 days and used for comparison of values on a given day, thus allowing for adjustment of cut-off value to accommodate analytical variability. Our established cut-off point for phenylalanine level was 180 μmol/l. At this cut-off level, 2.3% of all samples required reassaying and a repeat blood specimen was requested from 0.39% of the screened infants. The false-positive rate was 1:294 (0.34%). PKU was identified in 21 infants (1:6650), persistent non-PKU hyperphenylalaninemia in 5 infants (1:27,932) and transient hyperphenylalaninemia in 3 infants (1:46,554). No false-negatives are known to have occurred. This experience indicates that the phenylalanine fluorometric method we have developed is highly reliable and very useful for neonatal PKU screening.