Shortly after birth, a blood sample is taken from a newborn to screen for diseases such as phenylketonuria (PKU) and congenital hypothyroidism. This type of testing is important, because treatment is available to improve the health of the child. Newborn screening is required in the United States, but states vary on which tests they offer.

Examples of tests used for newborn screening include:

• Phenylketonuria (PKU) screen, which measures the amount of phenylalanine in a baby's blood. Babies found to have PKU should be put on a special low-protein diet to prevent intellectual disability.
• Cystic fibrosis test. Levels of immunoreactive trypsinogen (IRT), a digestive enzyme, are measured from a newborn's blood sample. Abnormally high levels of IRT suggest cystic fibrosis, although further testing is needed to confirm the diagnosis.
• Hemoglobin test, which tests for types of hemoglobin in a baby's blood that may point to sickle cell trait or sickle cell disease. Babies who have sickle cell disease need special medical care throughout their lives to treat the variety of problems that can be caused by the illness.

Other tests, such as newborn hearing tests, can tell whether a baby may need future hearing services or genetic testing. Approximately 50% of cases of newborn hearing loss are caused by genetic factors.¹