What is a heel stick test?
Before you leave the hospital with a newborn baby, your baby will be given what is commonly known as a “heel stick test”. This newborn screening is a blood test for certain inherited metabolic and endocrine disorders. What your baby is specifically tested for will certainly vary from state to state, but all babies nationwide are screened for at least three disorders — phenylketonuria (PKU), hypothyroidism and galactosemia. To find out what your state screens for visit the Natioanl Newborn Screening and Genetics Resource Center at http://genes-r-us.uthscsa.edu/
Even if you or your family members do not know of the existence of any genetic disorders in your family, your baby can still be at risk for having a genetic disorders. Because the disorders that are being screened for are usually extremely rare, your baby could be the first person in your family to be affected by a given disorder. It is important to give a baby the heel stick test, because these disorders could result in permanent disability, retardation, or death if left untreated.
The heel stick test is done within a few days of your baby’s birth. In a best case scenario, the test should be done during the first 48-96 hours of life. Breast milk and formula contain phenylalanine, the amino acid associated with the disorder PKU, and other amino acids associated with various metabolic disorders being screened for.
With these disorders, enzymes essential for your baby to break down certain amino acids are missing 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. Your baby’s heel will be pricked with a small point, and a few drops of blood will be taken for testing. The nurse will collect nine or ten drops of blood and place it on a piece of filter paper. This kind of sample is called a “blood spot” sample. The heel is used because it is the least sensitive part of your baby’s body.
The dried blood on the filter paper is sent to a laboratory and tested. Though some parents choose an early discharge from the hospital, it is best to have the heel stick test done after the first 48 hours of life. Testing earlier than 48 hours is not ideal, but if you’re going to leave the hospital early, you should have the screening done early. Early is much better than to not screen your new baby at all. Don’t be surprised if your baby has to undergo the testing more than one time — many hospitals and doctors will recommend having a second screening performed to ensure that baby’s screening results are accurate.
There are about twenty-nine disorders that doctors recommend 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. This information is taken from WebMD.com:
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 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).
The screening results for your baby 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 — do not worry, this is good news. If your baby has tested positive for any of the disorders, your baby will need additional testing and treatment. The tests are designed to be extremely sensitive, so follow up tests even after a “positive” result commonly show that baby is completely healthy. Follow up testing may include a referral to a genetic specialist or a pediatrician that specializes in endocrine or metabolic disorders.