Guthrie Test:The Guthrie test is a straightforward blood screening test designed for detecting phenylketonuria (PKU). It was a pioneering development in newborn metabolic screening. In 1958-59, Dr. Robert Guthrie (1916-95) was tasked with creating an easy way to monitor blood phenylalanine levels. He devised the test in just three days, utilizing a "bacterial inhibition assay."To perform the test, a drop of blood on filter paper is placed on an agar plate that contains a bacteria growth inhibitor. However, this inhibition can be overcome by high levels of phenylalanine. After leaving the agar plate to incubate overnight, the size of the bacterial growth around the test disc is compared to a control disc containing a known amount of phenylalanine. This comparison allows for an estimation of the phenylalanine concentration in the test sample.Dr. Guthrie used a common strain of the soil bacterium Bacillus subtilis, with the inhibitor being 2-thienylalanine, which suppresses B. subtilis growth, an effect reversed by phenylalanine. Guthrie's initial agar dish was actually a Pyrex baking pan.Beyond PKU, Guthrie developed similar bacterial inhibition assays for other genetic disorders like maple syrup urine disease, galactosemia, and homocystinuria. These tests are straightforward, cost-effective, and ideal for screening large numbers of samples.In the United States, the primary laboratory techniques now employed include the Guthrie bacterial inhibition assay (BIA), fluorometric analysis, and tandem mass spectrometry, all of which are reliable for detecting PKU.For more information, see phenylketonuria.