Detection Test

1. Blood phenylalanine: Tested by chromatography but Tandem Mass Spectroscopy is more relaible but expensive. Normal level is 1mg/dl but in PKU, level is more than 20mg/dl.
2. Guthrie Test (shown in the picture above): Also known as Neonatal Heel Pricking and it is a rapid screening test. Uses Bacillus subtilis that requires phenylalanine as a growth factor. This bacteria will be spread on a specially-prepared agar and small disc containing the infant's blood will be placed on the agar. If there is presence of phenylalanine, this compound will diffuse into the agar and promote the growth of the bacteria.
3. Ferric Chloride Test: Ferric chloride is added to the patient's urine containing phenylketones. Transient blue-green colour will indicate that the patient is positive for PKU. However, this method is less reliable.