Don't skip newborn screening
DEAR MAYO CLINIC: I'm nearing the end of my third pregnancy and curious about what kinds of tests my newborn baby will have once she arrives. My other children had blood taken after they were born, but I never felt comfortable asking what it was for. What are the doctors looking for exactly? Are these tests necessary?

ANSWER: The blood taken from your baby after she's born will be examined to find out if she has any of a variety of treatable conditions. This procedure, called newborn screening, is very important because these conditions can be most effectively treated when they are identified early, before symptoms appear.

Newborn screening involves taking a small sample of blood by pricking the baby's heel (heel stick). Usually, the procedure is done on the second day of life. The blood sample is placed on a piece of filter paper, dried and sent to a laboratory. There, the blood is analyzed for specific markers that, if abnormally high or low, suggest the baby has a certain condition. Many of the conditions included in newborn screening may not otherwise be detected before a baby develops disabling or life-threatening symptoms. Newborns with these disorders typically don't show any symptoms at birth.

After testing is completed, any blood remaining from the sample is either discarded or stored, depending on the laws regulating each state's newborn screening program. Stored samples can only be retrieved with written consent from the patient or legal guardian, or for the purpose of research studies involving a large number of leftover samples with approval of the state's ethics review board and only after samples have been made anonymous.

Newborn screening was initiated as a public health program by Dr. Robert Guthrie (the screening is sometimes referred to as the "Guthrie test") in New York State more than 40 years ago. The original purpose of newborn screening was to identify babies who had phenylketonuria (PKU). This amino acid disorder causes mental retardation unless the baby is placed on a diet that restricts the amino acid phenylalanine within the first few weeks of life. If it is detected and addressed soon after birth, though, babies with PKU typically have no complications from the disorder.

Today, all states in the U.S. require newborn screening, although the number and type of conditions screened for varies. Until recently, there was no unified approach regarding which conditions to screen for and when to add new conditions to the screening panel.

However, in 2006, the American College of Medical Genetics developed the Uniform Panel, consisting of 54 genetic conditions, and recommended that every newborn in the country be screened for at least 29 of those conditions. Ninety-nine percent of children born in the United States now are screened for at least the 29 primary target conditions. For a condition to be included in the panel, a reliable screening measure needs to be available and effective treatment established for the disorder, among other criteria.

In addition to PKU, another disorder commonly included in newborn screening is medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, a condition that affects the metabolism of fat. Although MCAD deficiency can be life-threatening if it goes undetected, once it is identified, treatment usually requires only minor dietary monitoring.

Other disorders usually in the newborn screening panel are congenital hypothyroidism -- a condition in which the thyroid gland doesn't produce enough of certain hormones; biotinidase deficiency -- babies with this condition don't have enough biotinidase, an enzyme that recycles the B vitamin biotin; sickle cell anemia -- a blood disease; and congenital adrenal hyperplasia -- a family of genetic conditions affecting the adrenal glands that can interfere with normal growth and development.

The good news is, these and the other inherited disorders included in newborn screening are rare. An estimated 1 in every 2,000 to 3,000 babies is affected with one of these conditions. So it's unlikely that your newborn will have any of them. But it's important for all babies to receive newborn screening, because if the test detects a genetic condition, early intervention and treatment can mean the difference between a child who is healthy and one who has lifelong health issues.

If you have questions about newborn screening, or want to find out which conditions your state screens for, talk to your doctor or contact your state's department of health for more information. More information also is available at the National Newborn Screening and Genetics Resource Center Web site (http://genes-r-us.uthscsa.edu/resources/consumer/statemap.htm). -- Dietrich Matern, M.D., and Piero Rinaldo, M.D., Ph.D., Biochemical Genetics Laboratory, Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minn.