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Newborn screening tests

Definition

Newborn screening tests look for serious developmental, genetic, and metabolic disorders so that important action can be taken during the critical time before symptoms develop. Most of these illnesses are very rare.

In the United States, individual states regulate newborn screening, so the diseases screened for vary considerably from state to state. Most states require three to eight tests, but organizations such as the March of Dimes and the American College of Medical Genetics suggest more than two dozen additional tests.

The most thorough screening panel checks for about 40 disorders. All 50 states screen for congenital hypothyroidism, galactosemia, and phenylketonuria (PKU).

Alternative Names

Infant screening tests; Neonatal screening tests

How the test is performed

Blood tests: A health care professional will prick the baby’s heel to obtain a few drops of blood. The blood is sent to a lab for analysis.

Hearing test: An audiologist will place a tiny earpiece or microphone in the infant’s ear or stick electrodes on the baby’s head.

How to prepare for the test

There is no preparation necessary for newborn screening tests. The tests are performed when the baby is between 24 hours and 7 days old, typically before the baby goes home from the hospital.

How the test will feel

The baby will most likely cry when his or her heel is pricked to obtain the small blood sample. The hearing test should not cause the baby to feel pain, cry, or respond.

Why the test is performed

Screening tests do not diagnose illnesses. They identify which babies need additional testing to confirm or rule out illnesses. Good screening tests have a low false-negative rate (if the test is normal, the child should be healthy), but may have a high false-positive rate (as many affected children as possible should test positive, even if this means many healthy children also test positive).

If follow-up testing confirms that the child has a disease, appropriate treatment can be started right away, before symptoms appear.

Screening tests are used to detect a number of disorders, including:

• Amino acid metabolism disorders:
  • Arginosuccinic acidemia
  • Citrullinemia
  • Homocystinuria
  • Maple syrup urine disease
  • Phenylketonuria (PKU)
  • Tyrosinemia type I
• Biotinidase deficiency
• Congenital adrenal hyperplasia
• Congenital hypothyroidism
• Cystic fibrosis (see also: Neonatal cystic fibrosis screening)
• Fatty acid metabolism disorders:
  • Carnitine uptake deficiency
  • Long-chain L-3-hydroxyacyl-CoA dehydrogenase deficiency
  • Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency
  • Trifunctional protein deficiency
  • Very long-chain acyl-CoA dehydrogenase deficiency (VLCAD)
• Galactosemia
• Glucose-6-phosphate dehydrogenase deficiency (G6PD)
• Human immunodeficiency disease (HIV)
• Organic acid metabolism disorders:
  • 3-Hydroxy-3-methylglutaric aciduria (HMG)
  • 3-Methylcrotonyl-CoA carboxylase deficiency (3MCC)
  • Beta ketothiolase deficiency
  • Glutaric acidemia type I
  • Isovaleric acidemia
  • Methylmalonic acidemia
  • Multiple carboxylase deficiency (MCD)
  • Propionic acidemia
• Sickle cell disease and other hemoglobinopathy disorders and traits
• Toxoplasmosis

See also: Hearing loss - infants

Normal Values

Normal values for each screening test may vary depending on how the test is performed.

What abnormal results mean

An abnormal result means that the child should have additional testing to confirm or rule out the condition.

What the risks are

Risks for the newborn heel prick blood sample include pain and possible bruising at the site where the blood was obtained.

Special considerations

Newborn testing is critical for the baby to receive treatment that may be life saving. However, not all disorders that can be detected by the screening tests can be treated.

Although states do not perform all screening tests, parents can have  additional tests done by qualified laboratories at large medical centers. Private laboratories also offer newborn screening. Parents can find out about extra newborn screening tests from their physician or hospital where the baby will be born, as well as through organizations like the March of Dimes.

References

American College of Medical Genetics Newborn Screening Expert Group. Newborn screening: toward a uniform screening panel and system--executive summary. Pediatrics. 2006 May;117(5 Pt 2):S296-307.

Lin KW. Screening for sickle cell disease in newborns. Am Fam Physician. 2009;79(6):507-8.

Pesce MA. Laboratory Testing in Infants and Children. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th Ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 714.

Smith L. Updated AAP Guidelines on Newborn Screening and Therapy for Congenital Hypothyroidism. Am Fam Physician. 2007; 76(3).