A universal screening test in which a spot of blood is extracted by means of a heel prick, and which is carried out in the newborn period (usually on day 2) to detect treatable conditions such as phenylketonuria (PKU) or congenital hypothyroidism, conditions which can lead to irreversible brain damage, if not treated early. The test was devised by Robert Guthrie (1916-1995) in 1959, three days after being asked to develop a simple method for the monitoring the level of phenylalanine in the blood, using a common, standardised strain of soil bacterium (Bacillus subtilise). He went on to develop further assays for other inherited disorders of metabolism, including galactosemia (a defect in the body’s ability to use the sugar galactose), maple syrup urine disease (disease of amino acid metabolism that leads to acidosis, and urine that smells like sweet like maple syrup),.and homocystinuria (a disorder in the metabolism of the amino acid methionine).