Understanding the Guthrie Test Given to Newborns

Have you ever wondered exactly what the medical staff is doing when the prick the heel of a newborn baby and take a blood sample on a small card? In fact, the test has a name - it's called the "Guthrie Test" and it serves an important function. The Guthrie Test began as a simple way to screen for the metabolic disorder phenylketonuria or PKU. The test is the precursor to newborn metabolic screening - which can detect disorders soon after birth.

The test was invented in 1958 by Dr. Robert Guthrie (1916-1995). Dr. Guthrie was asked to develop a simple method to monitor the blood phenylalanine level (also known as "phe"). It took him only three days to develop the test and it they type of test referred to as a "bacterial inhibition assay."

The test involves pricking the baby's heel to obtain a blood sample. The sample is pressed onto a card and exposed special reagents that react to a raised phenylalanine level. The blood on the filter paper cared is placed on the surface of an agar plate containing a substance that inhibits the growth of bacteria. If there are high levels of phenylalanine, it will interfere with the inhibition. The blood sample will actually be left overnight and then the growth zone on the card will be compared with a negative sample to determine whether phenylketonuria is present.

Originally, Dr. Guthrie used a common strain of soil bacterium (Bacilus subtilis). With the creation of this successful test, Dr. Guthrie went on to create and develop bacterial inhibition assays for other inherited metabolism disorders and diseases. This type of testing has the advantage of being simple, inexpensive and well-adapted to screening large numbers of individuals such as in a hospital setting.

The Guthrie Test has been part of typical newborn screening since the 1960's and has been used widely in the United States and Europe. It is gradually being replaced, however, by techniques that can detect more congenital disorders and defects such as the tandem mass spectrometry. So, while the Guthrie Test has been a standard in newborn screenings for two generations, it may eventually be completely replaced by more technological procedures.

For more information about The Guthrie Test, the online resource of Answers.com can provide an overview, as well as links to related terms, tests and screenings - and other pertinent information. The Science and Technology Dictionary site is available at http://www.answers.com/topic/guthrie-test.