1 Massachusetts Metabolic Disorders Program, State Laboratory Institute 305 South Street Jamaica Plain, MA 02130
2 New England Hypothyroidism Screening Program, State Laboratory Institute 305 South Street Jamaica Plain, MA 02130
Newborn screening for phenylketonuria (PKU) is now so firmly established in North America and in many other areas of the world that it is a bit difficult for most pediatricians to recall when PKU was diagnosed on the basis of mental retardation. The key to PKU screening has been the Guthrie test, the genius of which is not the bacterial assay that is employed (though this assay was certainly a momentous development) but the simple filter paper blood specimen. This specimen, easily obtained by blotting a few drops of blood from the heel of a neonate, is even more easily mailed to a central laboratory for testing.