Screening blood tests on newborns can identify important metabolic and endocrine disorders before symptoms ever appear. Left  undetected, these disorders can result in seizures, stunted growth or even death. Before such tests were available, some babies  developed serious health problems, including mental retardation, that were irreversible.

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) screening, which tests for phenylalanine in a baby's blood. Babies found to have PKU should be put on a special low-protein diet to prevent mental retardation.

Newborn screening for cystic fibrosis. Levels of immunoreactive trypsinogen (IRT), a digestive enzyme, are measured from a blood sample. Abnormally high levels of IRT suggest CF, although further testing is needed to confirm the

diagnosis.

Sickle cell testing, which tests for sickle hemoglobin in a baby's blood. 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 indicate the need for further hearing services as well as genetic testing. Approximately 50% of cases of newborn hearing loss are caused by genetic factors.

If the disorders are detected and treated early enough, however, they can be controlled or may be successfully treated. Newborn screening is widely used to detect many disorders and a newer laboratory technique, tandem mass spectrometry, has increased the number of diseases that can be identified in newborns. Babies who would've developed life-threatening health problems or mental retardation now are able to grow up as healthy children.