Repeat the test regardless of the results on initial screening. Repeat the test if McCamon-Robins fluorometric assay was used. Newborn PKU screening in the United States is performed with the Guthrie inhibition assay 7 or the McCamon-Robins fluorometric test. Both tests can be performed on blood spotted on filter paper, and both are highly accurate. The laboratory that performs the PKU test has the responsibility of reporting the results to the physician and to the facility where the infant was born.
Some laboratories also notify the parents.
The American Academy of Pediatrics recommends that a PKU screening test be repeated by two weeks of age if it was performed before the newborn was 24 hours of age. However, a second test is not necessary if the initial PKU screening is performed with the McCamon-Robins fluorometric test 8 when the newborn is between 12 and 24 hours of age. Not all states, however, use 2 mg per dL as the cut-off value. Breast milk contains only 12 to 14 mg of phenylalanine per ounce, compared with 24 to 28 mg per ounce in formula. Because PKU is a heterogeneous disorder, phenylalanine levels vary greatly in infants with the disease.