Robert Guthrie developed a method to test infants for phenylketonuria (PKU) in the United States during the twentieth century. PKU is an inherited condition that causes an amino acid called phenylalanine to build to toxic levels in the blood. Untreated, PKU causes mental disabilities. Before Guthrie’s test, physicians rarely tested infants for PKU and struggled to diagnosis it. Guthrie’s test enabled newborns to be quickly and cheaply screened at birth and then treated for PKU if necessary, preventing irreversible neurological damage. After developing the test, Guthrie traveled the world to advocate for mass screening for PKU in newborns. Along with his PKU test, Guthrie developed newborn screens for maple syrup urine disease and for galactosemia. Guthrie’s test for PKU and campaign for newborn screening led to the early diagnoses of PKU in thousands of infants, preventing those infants from developing mental disabilities.

The Guthrie test, also called the PKU test, is a diagnostic tool to test infants for phenylketonuria a few days after birth. To administer the Guthrie test, doctors use Guthrie cards to collect capillary blood from an infant’s heel, and the cards are saved for later testing. Robert Guthrie invented the test in 1962 in Buffalo, New York. Phenylketonuria (PKU) is a congenital birth abnormality in which toxic levels of the amino acid phenylalanine build up in the blood, a process that affects the brains in untreated infants. Guthrie’s test detects phenylalanine in the blood of newborns, enabling for early diagnosis of PKU. Early diagnoses of PKU prevent the development of mental disabilities in the thousands of individuals affected each year.