Fifteen-year experience with screening for phenylketonuria with an automated fluorometric method

An automated fluorometric method, rather than the Guthrie test, has been used in North Carolina for neonatal screening for phenylketonuria (PKU). Although there is no testing law, 97% of newborn infants are screened. Twelve children with PkU, not referred for dietary management, were born before the screening program was established, were born elsewhere, or were successfully identified at birth but not referred for treatment. None was missed because of laboratory error or because of the lack of a testing law. Positive skewing was noted among initial blood phenylalanine levels of 49 infants with PKU and severe hyperphenylalaninemia. Log transformations caused the values to be normally distributed and permitted the calculation of tolerance and confidence limits. These provided estimates of the percentage of phenylketonuric infants whose initial blood levels might fall below any given cutoff value.