Newborn health screening

Screening for newborn babies

The purpose of newborn screening is to recognize diseases that cause lifelong health issues or mortality before the onset of symptoms. These disorders include inborn metabolism deficiency, endocrine disorders, hemoglobinopathies, immunodeficiency, cystic fibrosis, and critical congenital heart defects. Early treatment of these rare conditions may significantly decrease mortality and morbidity in afflicted patients. 

Congenital and genetic disorders

Various conditions that may be present at birth (congenital) can affect the health and wellness of a newborn. Most of these conditions are rare, though some are more prevalent in certain families or ethnic groups. Disorders range from difficulties processing certain nutrients (metabolic), to problems with hormones (endocrine), to the production of abnormal forms of hemoglobin, the oxygen-carrying protein in red blood cells. Some of these conditions cannot be cured, but many can be managed so that the child can grow and live a relatively normal life.

Newborn screening tests help to identify potentially treatable or manageable congenital disorders within days of birth. Life-threatening health problems, mental retardation, and serious lifelong disabilities can be avoided or minimized if a condition is quickly identified and treated.

Newborns can be routinely screened for many of these disorders before leaving the hospital using a few drops of blood.  

Screening tests recommended for all newborns

It is recommended[1] that all newborns be screened for 34 core disorders and 26 secondary disorders. The tests are organized into broad categories:

·         Metabolic disorders (e.g., phenylketonuria, PKU)

·         Endocrine disorders (e.g., congenital hypothyroidism [CH] and congenital adrenal hyperplasia [CAH])

·         Hemoglobin disorders (e.g., sickle cell anemia)

·         Other disorders (e.g., cystic fibrosis, severe combined immunodeficiencies (SCID))

Special collection techniques should be used with newborns to minimize discomfort during specimen collection. In most cases, all the tests can be done using just a few drops of blood obtained from a pricked heel.

Newborn screening tests are usually performed within 24 to 48 hours of life. For some tests, such as phenylketonuria (PKU) and congenital hypothyroidism (CH), it is important that they not be run too soon after birth. They may not accurately reflect whether a disorder is present if performed within the first 24 hours of life. Since women and their newborns may be discharged within a day or two of the birth, it is possible that a newborn could be tested with a sample taken within those first 24 hours. Consequently, some routinely recommend screening two times, once in the hospital and then about 2 weeks later. This second screen is done to maximize the accuracy of testing.

Table of 34 Core Disorders

Screening for inherited disorders in newborns at risk

Screening tests for certain inherited diseases that are not already covered by mandatory screening may be requested based on family history or ethnic background. Testing typically involves detecting the specific gene mutation(s), or change in DNA, associated with a disorder that occurs frequently within a family or members of a specific ethnic group.

Family history: When parents are concerned that a certain disease runs in their families (e.g., Duchenne muscular dystrophy, fragile X syndrome, or other chromosomal abnormalities), they may request that their newborn be tested for the disease. While testing for cystic fibrosis may be ordered because of family history, for example, its frequency in the population at large means that testing is now recommended for all newborns. Newborn screening program includes a test for CF, although the method used may vary, with some performing only a test to determine the blood level of a chemical called immunoreactive trypsinogen (IRT) and others performing both an IRT and a DNA test to check for mutations or changes in the CF gene.

Ethnic group: When the parents are concerned because a certain disorder is common among their ethnic groups (e.g., Tay-Sachs disease, thalassemia, sickle cell anemia, cystic fibrosis, or congenital adrenal hyperplasia (CAH)), they may request that their newborn be tested.

Other risks: Less frequently, some healthcare providers or parents request that the newborn’s DNA be tested to identify a condition or risk of developing a condition that may not become evident or have an effect until later in life (e.g., Huntington disease, type 1 diabetes, and some forms of breast, ovarian, and colon cancer). Some parents value the information and want to be on the lookout for improvements in diagnosis, prevention, and treatment.

In some cases, one or both of the parents can be tested before or during a pregnancy to determine if they are carriers of these gene-based disorders. Amniotic fluid can also sometimes be tested during the pregnancy.

Genetic tests can be run on blood, other types of body fluids, and tissues. For some conditions, chromosomes are examined for abnormalities; for other diseases, a single gene is analyzed. It should be noted that some genetic tests will identify a condition for which there is no treatment or cure and no changes can be made to improve the child’s quality of life. The value of such test results is controversial.

Infectious Diseases

Typically, newborns are tested for infectious diseases only if they show signs and symptoms. Usually HIV or hepatitis B screening tests are only performed if it is known that the mother has the disease or if she was not tested during the pregnancy and therefore her disease status is unknown. Treatment can be administered soon after birth to protect the health of the newborn.

Human immunodeficiency virus

 HIV is the virus that causes AIDS (acquired immunodeficiency syndrome). The infection can pass from an infected mother to her child during pregnancy, delivery, or breastfeeding.

Most AIDS cases in children result from mother-to-baby transmission. If a mother with HIV does not receive treatment during the pregnancy, the child has a 1 in 4 chance of getting HIV. With timely treatment, however, fewer than 2% of children of infected mothers get the virus.

Hepatitis B

It is recommended that all pregnant woman be screened for hepatitis B infections either before or early in her pregnancy regardless of previous hepatitis B vaccination or previous negative hepatitis B (HBsAg) test result. Women at increased risk of hepatitis B infection, such as those with intravenous drug use, should be screened again at delivery.

With the advent of screening pregnant women for hepatitis B and the vaccination of newborns, the number of infected babies has fallen. However, a newborn may be screened if there is concern that the mother is at high risk of infection and/or she was not tested during the pregnancy.

References:

1.    https://labtestsonline.org/screenings/newborns

2.    https://www.nhs.uk/conditions/baby/newborn-screening/blood-spot-test/

3.    Alex R Kemper, Newborn screening, UpToDate, 2018.