Newborn "Heel Stick" Screening (Newborn Genetic Screening)
National Newborn Screening and Genetics Resource Center.
Why does my baby need the heel stick test?
You may be thinking, I don’t have any of these disorders in my family, so why does my baby need to be screened? Even if you do not know of a direct family member with a genetic disorder, your baby may still be at risk for having one of these genetic disorders. Because the disorders that are being screened for are rare, your baby could be the first baby in your family to have this disorder. It is important to test because these disorders left untreated could result in permanent disability, mental retardation or death.
How is the newborn heel stick test performed?
The heel stick test is done within a few days of your baby’s birth. Ideally the test should be done during the first 48-96 hours of life. Breast milk and formula contain phenylalanine, the amino acid associated with PKU, and other amino acids associated with other metabolic disorders being screened. With these disorders, enzymes essential in breaking down certain amino acids are missing, deficient, or defective. Although some of the disorders being screened are not amino acid disorders, it is best for baby to be receiving breast milk or formula for 48 hours to ensure all screenings are the most accurate. The test is generally done right before baby is discharged. Baby’s heel will be pricked and a few drops of blood will be taken. The nurse will collect nine or ten drops of blood and place it on a filter paper. The sample is called a “blood spot”. The dried blood on the filter paper is sent to a laboratory and tested. Some moms choose to have an early discharge from the hospital. Although testing earlier than 48 hours is not ideal it is much better to screen a little early then to not screen at all. Many hospitals and doctors recommend having a second screening to ensure that baby’s screening results are accurate.
What metabolic and endocrine disorders will they be checking for?
There are about twenty-nine disorders that the March of Dimes recommends screening for. Some states screen for that many and others only screen for three or four disorders. The disorders are grouped into five different categories.
- Amino acid metabolism disorders Babies with amino acid metabolism disorders, as the name suggests, have problems metabolizing certain amino acids. Babies born with amino acid metabolism disorders have missing or defective enzymes that metabolize proteins. The amino acids either are not broken down or the body cannot transport the amino acids into the cells. As a result, amino acids or nitrogen (a component of amino acids) build up in the body to toxic levels. Amino acid metabolism disorders include Phenylketonuria(PKU), Maple syrup urine disease (MSUD), Homocystinuria (HCY), Citrullinemia (CIT), Argininosuccinic academia (ASA), and Tyrosinemia type I (TYR I).
- Organic Acid Metabolism Disorders Babies with organic acid metabolism disorders cannot process certain branched amino acids. Babies born with this disorder do not produce the enzymes or have malfunctioning enzymes that do not break down these amino acids properly. As a result, organic acids build up to toxic level in the body. Some organic acid metabolism disorders that your baby might be screened for are Isovaleric academia (IVA), Glutaric acidemia type I (GA I), and Hydroxymethylglutaric aciduria or HMG-CoA lyase (HMG).
- Fatty Acid Oxidation Disorders Fatty acid oxidation refers to the way your body breaks down fat. Fat is broken down in several steps and requires a number of enzymes. If one of the enzymes in this process is not working properly the body cannot turn fat into energy for the body. The body’s main source of energy is glucose, but if there is no glucose available, your body turns to fat for energy. Babies with fatty acid oxidation disorders have malfunctioning enzymes so their bodies cannot turn fat into energy. Some examples of fatty acid oxidation disorders that your baby might be screened for are Long Chain 3-Hydroxyacyl-CoA Dehydrogenase Deficiency (LCHAD), Medium Chain Acyl-CoA Dehydrogenase Deficiency (MCAD), Short Chain Acyl-CoA Dehydrogenase Deficiency (SCAD), Trifunctional Protein Deficiency (TFP Deficiency), or Very Long Chain Acyl-CoA Dehydrogenase Deficiency (VLCAD).
- Hemoglobinopathies and sickle cell disease Hemoglobinopathies and sickle cell disease are disorders caused by abnormal hemoglogin, a protein in red blood cells that is responsible for transporting oxygen to the body. Babies with these hemoglobinopathies may have problems with red blood cell production resulting in anemia (shortage of red blood cells) or produce abnormally shaped red blood cells that cause problems in blood circulation and damage easily. These disorders include sickle cell anemia, Thalassemia, and Hb S/C disease.
- Other disorders Other disorders your baby might be screened for include Congenital hypothyroidism (a hormone deficiency that causes problems with growth and brain development), Biotinidase deficiency, Congenital adrenal hyperplasia (an endocrine disorder that affects hormone production from the adrenal gland), or Cystic Fibrosis (a life threatening disease that causes mucous secretions in the lungs to become thick causing severe respiratory problems).
What happens if my baby tests positive for one of the disorders in the newborn screening?
The screening results usually come back within a few days. You may not hear anything about the screening if your baby does not test positive for any disorders. If your baby has tested positive for any of the disorders, your baby will need additional testing. The tests are designed to be extremely sensitive so often follow up tests show that baby is healthy. Follow up testing may include a referral to a genetic specialist or a pediatrician that specializes in endocrine or metabolic disorders.
Resources for information on newborn screening or genetic disorders:
- National Newborn Screening and Genetics Resource Center
- March of Dimes
- Organic Acidemia Association
- Fatty Acid Oxidation Disorders Support
- The National Coalition for PKU & Allied Disorders