Newborn Screening

Newborn screening (NBS) is a public health program that tests all newborns for a panel of serious, treatable conditions in the first days of life. Using dried blood spots collected via heel prick, tandem mass spectrometry and other assays detect metabolic, endocrine, hemoglobin, and other disorders before clinical symptoms appear, enabling early intervention to prevent disability or death.

• Dried blood spots (DBS): Blood is collected by heel prick onto filter paper (Guthrie card), typically at 24–48 hours of life. Some states require a second screen at 1–2 weeks. DBS can be stored and used for confirmatory testing or future research (with consent considerations).

• Tandem mass spectrometry (MS/MS): The primary technology for NBS. Measures acylcarnitines and amino acids simultaneously, enabling detection of dozens of metabolic conditions in a single assay. Disorders detected include fatty acid oxidation defects (e.g., MCADD, VLCADD), organic acidemias (e.g., propionic acidemia, methylmalonic acidemia), and amino acidopathies (e.g., PKU, maple syrup urine disease).

• Other NBS assays:

  • Immunoreactive trypsinogen (IRT): Screening for cystic fibrosis. Elevated IRT triggers reflexive CFTR DNA analysis.
  • TSH/T4: Congenital hypothyroidism
  • 17-hydroxyprogesterone (17-OHP): Congenital adrenal hyperplasia (21-hydroxylase deficiency)
  • Hemoglobin electrophoresis / HPLC: Sickle cell disease and other hemoglobinopathies
  • Biotinidase enzyme activity: Biotinidase deficiency
  • Galactose-1-phosphate uridylyltransferase (GALT): Galactosemia
  • TREC assay (T-cell receptor excision circles): Severe combined immunodeficiency (SCID)
  • Pulse oximetry: Critical congenital heart disease (CCHD), a point-of-care screen, not a blood test
  • Hearing screen: Universal newborn hearing screening via otoacoustic emissions or auditory brainstem response

• Recommended Uniform Screening Panel (RUSP): A federal advisory committee (ACHDNC) maintains the RUSP, which recommends a core panel of conditions for all states to screen. As of 2025, includes ~35 core conditions and ~25 secondary conditions. Recent additions include SMA (spinal muscular atrophy), MPS I (Hurler syndrome), MPS II (Hunter syndrome), Pompe disease, and X-linked adrenoleukodystrophy (X-ALD).

• State variation: NBS is mandated at the state level, not federally. States may screen for more or fewer conditions than the RUSP recommends. Families who move between states or deliver in different states may have different screening panels.

• Confirmatory testing workflow: A positive NBS result is a screening result, not a diagnosis. Confirmatory testing includes: (1) Repeat NBS if initial result is borderline; (2) Quantitative plasma amino acids or urine organic acids for metabolic disorders; (3) Sweat chloride test for CF; (4) Hemoglobin electrophoresis for hemoglobinopathies; (5) Molecular/genetic testing for definitive diagnosis.

• Early treatment saves lives: NBS identifies treatable conditions in the presymptomatic period. For example, early dietary management of PKU prevents intellectual disability; early treatment of SCID with bone marrow transplant can be curative.
• Genetic counseling implications: Positive NBS results generate significant parental anxiety. Genetic counselors play a key role in explaining the difference between a screening result and a diagnosis, facilitating confirmatory testing, and providing recurrence risk counseling.
• Carrier detection: NBS may incidentally identify carriers (e.g., sickle cell trait, CF carriers). This has counseling implications for the family.
• False negatives exist: NBS is not 100% sensitive. A normal NBS does not rule out a genetic condition. Clinicians should pursue diagnostic testing if clinical suspicion is high, regardless of NBS results.

• False positives are common: NBS has a high false positive rate, particularly for metabolic conditions. This creates parental anxiety and requires prompt follow-up to avoid unnecessary treatment.
• Not all conditions are on every state's panel: Screening coverage varies by state. Some treatable conditions may not yet be included.
• Timing-sensitive: Collection before 24 hours of life increases false positive rates (especially for CAH) and may cause false negatives (e.g., inadequate protein intake for PKU detection). Premature and transfused infants may need repeat screening.
• Does not detect all genetic conditions: NBS screens for a specific panel of conditions. Many genetic disorders (including most chromosomal, structural, and neurological conditions) are not part of NBS.
• Ethical considerations: Long-term storage of DBS raises privacy concerns. Opt-out policies and consent for secondary research use vary by state.