The newborn screening model is fairly straightforward. Typically, before the infant is discharged from the hospital (around 24 to 36 hours of age), heel stick blood is placed on special filter paper, dried, and mailed to the state health department for testing. Medical and laboratory research has led to the discovery that other diseases could also be screened in newborns using these dried blood specimens. Currently, all states and the District of Columbia test all newborns for at least PKU and congenital hypothyroidism. There are generally five criteria to satisfy before a disease is considered appropriate for newborn screening: 1. The disease must be well defined and serious enough to justify mass screening; 2. There must be an accurate testing method available; 3. The cost of the test must be reasonable; 4. There must be available treatment for the disorder; and 5. There must be adequate medical management facilities to refer infants for confirmatory diagnosis and treatment. Although newborn screening is often classified as genetic screening, these criteria do not require that the screened disorder have a genetic origin. In fact, congenital hypothyroidism, which is part of every newborn screening program in this country, is usually not a genetic disease.
John M. Naber & David R. Johnson, Mandatory HIV Testing Issues in State Newborn Screening Programs, 7 J.L. & Health 55 (1992-1993)