Guthrie test (also known as heel prick test) is a test that helps in early detection of phenylketonuria (PKU) in neonates. It was first discovered by Dr. Robert Guthrie, a microbiologist and a physician. It is called heel prick test because blood samples for the test are usually taken from the heels of the newborn.
Phenylketonuria (PKU) is rare genetic disorder and an inborn error of metabolism of the amino acid – phenylalanine. This is as a result of deficiency of phenylalanine hydroxylase (enzyme that metabolizes the amino acid, phenylalanine), thereby leading to an increase/rise in the level of phenylalanine in the blood. The high concentration of phenylalanine in the blood can cause mental disability, brain damage or seizures at early age of the neonate or later in life. Hence, early detection of this condition is very important as it gives a better prognosis.
Phenylalanine occurs naturally in many protein-rich foods, such as milk, eggs and meat. Phenylalanine also is sold as a dietary supplement. The artificial sweetener, aspartame, which is added to many medications, diet foods and diet sodas, contains phenylalanine. Such foods and medications containing phenylalanine must be severely restricted or avoided in PKU patients.
NOTE: Guthrie test is usually done within few days (5-8 days) of neonatal life. It’s a routine test for all neonates before leaving the hospital.