Newborn screening refers to the screening of blood samples taken from newborn infants to test for genetic and metabolic disorders that can become life threatening or cause impaired growth and development later in life.
The main goal of this type of screening is to begin early treatment if a disorder is present in order to minimize or prevent any serious outcomes of the condition. The frequency of abnormalities detected on newborn screening is 1 for every 1000 babies tested. Newborn screening is usually provided free of charge in most countries where it is recommended.
Collection of blood
Parents' consent is obtained before blood samples are taken and parents are also provided with an information booklet on the pros and cons of getting their babies tested for the diseases.
Since the total volume of blood is very low in babies and collection may be a challenge, blood is collected by way of a heel-prick using a sterile hypodermic needle. The sampling is performed around 48 to 72 hours after birth.
Drops of the blood collected are placed on the filter paper part of a "newborn screening card" to form blood spots which can be analysed when the card is sent to a laboratory. The remainder of the card contains important details about the baby such as weight, gender, time of first feeding as well as the parents' contact information.
The card is stored after testing and is only destroyed after a fixed period that is determined by state or country laws.
Outcome of the testing
For the majority of babies, the test results are negative. However, for babies who do test positive, further confirmatory tests are performed.
Conditions likely to be screened
In most countries, the conditions that newborns are commonly screened for include:
Primary congenital hypothyroidism - This is a serious but treatable condition that affects approximately 1 in 4000 babies. The thyroid gland is either abnormal or absent leading to inadequate production enough of the thyroid hormone, which is essential for growth and development.
Testing and diagnosis are important at birth since there may be no symptoms and the condition is treatable with thyroid hormone replacements. If the condition is not treated it may result in abnormal growth and mental retardation. Congenital hypothyroidism is not usually inherited and may occur spontaneously.
Cystic fibrosis - This is a genetic disorder that mainly affects the respiratory and gastrointestinal system. The disease occurs in around 1 in 2500 babies and is an autosomal recessive condition.
The condition is caused by a mutation in the gene that codes for a protein called the cystic fibrosis transmembrane conductance regulator. This protein is responsible for regulating the transfer of chloride and sodium ions across cell membranes, therefore determining the composition of sweat, mucus and digestive fluids. Reduced function of CFTR results in a thick sticky mucus building up in bodily passages such as the airways and pancreatic duct and causes blockage, infection and inflammation.
All babies are tested for cystic fibrosis around 6 days after birth. A heel prick blood test is performed to check levels of immunoreactive trypsinogen (IRT), which are raised in babies with the condition. If IRT levels are high, diagnosis is confirmed by way of genetic testing and a sweat test.
Phenylketonuria - This condition is one of the most common genetic metabolic conditions affecting newborns. The condition is caused by an absence of the active form of the liver enzyme phenylalanine hydroxylase which is responsible for the conversion of the amino acid phenylalanine to tyrosine. As a result, phenylalanine and its metabolites accumulate in the blood and brain and can cause brain damage.
This condition is inherited in an autosomal recessive manner. There are usually no symptoms at birth, making detection and early treatment important.
Galactosaemia - This is a rare metabolic disorder that affects 1 in 50,000 babies. A deficiency in the enzyme galactose-1-phosphate uridyltransferase leads to raised levels of galactose and galactose-1-phosphate in the body. Levels of galactose-1-phosphate become toxic in various tissues causing damage to various organs including the liver, kidneys and brain.
This condition also has an autosomal recessive pattern of inheritance. Newborns are screened for levels of galactose and galactose-1-phosphate in the blood. If the screening shows positive, the enzyme levels are then measured.
Other metabolic conditions - Around twenty other rare metabolic conditions can be detected using newborn screening.
Reviewed by Sally Robertson, BSc