Human Development

Newborn screening: state-mandated panels and follow-up

Clinical Overview and When to Suspect Newborn Screening Abnormalities

— Authorized under state law; federal Recommended Uniform Screening Panel (RUSP) currently lists 38 core conditions and 26 secondary conditions (HHS Advisory Committee on Heritable Disorders in Newborns and Children)

— States choose their own panels; most include all RUSP core disorders but variation exists — always check your state's specific panel

— Dried blood spot (DBS) heel-stick filter paper: metabolic, endocrine, hemoglobinopathies, immunodeficiencies, lysosomal storage disorders, SMA

— Point-of-care pulse oximetry: critical congenital heart disease (CCHD) at ≥24 hours of life

— Point-of-care hearing screen: otoacoustic emissions (OAE) or automated auditory brainstem response (AABR)

— Symptomatic infant (poor feeding, lethargy, jaundice, hypoglycemia, hypotonia, vomiting) + abnormal screen → treat as true positive until proven otherwise

— Family history of consanguinity, sibling neonatal death, prior affected child, or known carrier status

— Specific clinical clues: ambiguous genitalia + salt-wasting → CAH; persistent jaundice → galactosemia or biliary atresia; cataracts → galactosemia

— Optimal collection 24–48 hours of life, after protein feeding has begun (so phenylalanine, etc., have risen)

— Specimens drawn <24 h need a repeat at 1–2 weeks for several disorders (e.g., PKU, CAH)

— Premature, transfused, NPO, or sick infants require repeat testing per state protocol

Step 3 management: A "positive newborn screen" call from the state lab is a medical urgency, not a finished diagnosis — your job is to contact the family, examine the infant the same day, and initiate confirmatory testing and presumptive treatment when the disorder is time-sensitive (galactosemia, CAH, MSUD, MCAD).

Newborn screening (NBS) is a state-mandated public health program performed on virtually every U.S. newborn to detect treatable congenital disorders before symptoms appear

Three modalities are bundled into "newborn screening":

When to suspect a positive result is real, not a false positive:

Timing matters:

Presentation Patterns and Key History

— A normal exam does not rule out disease; treat the lab result, not the look of the baby

— Conversely, a symptomatic infant with a "pending" screen still warrants empiric workup

— Poor feeding + vomiting + lethargy in first week → urea cycle defect, organic acidemia, MSUD, galactosemia

— Jaundice with conjugated hyperbilirubinemia + hepatomegaly + E. coli sepsis → galactosemia (pathognomonic association)

— Salt-wasting crisis (hyponatremia, hyperkalemia, hypotension) at 1–2 weeks → 21-hydroxylase deficiency CAH

— Hypoglycemia with hypoketosis after fasting → MCAD or other fatty acid oxidation defect

— Sweet/maple-syrup odor of urine or cerumen → MSUD

— Mousy odor + eczema + developmental delay (later) → untreated PKU

— Recurrent infections + lymphopenia (ALC <2500) → SCID

— Progressive hypotonia + tongue fasciculations + areflexia → spinal muscular atrophy (SMA)

— Gestational age, birth weight, age at sample collection, transfusion or TPN status

— Feeding type (breast vs. formula — galactosemia infants worsen with lactose)

— Family history: consanguinity, ethnic background (sickle cell, Tay-Sachs, β-thal), prior unexplained infant deaths

— Maternal history: thyroid disease, steroid use (can suppress fetal HPA axis and confound CAH screen), gestational illness

— Maternal B12 deficiency → falsely elevated propionylcarnitine (mimics propionic acidemia)

— Maternal thyroid disease → transient neonatal hypothyroidism

— Antenatal steroids → suppressed 17-OHP, false-negative CAH screen

Board pearl: A breastfed infant with conjugated hyperbilirubinemia, hepatomegaly, hypoglycemia, and gram-negative sepsis is classic galactosemia — stop lactose immediately and switch to soy formula while awaiting confirmatory GALT enzyme assay.

Most infants with positive NBS are asymptomatic — that is the entire point of screening

Classic symptomatic presentations that should prompt immediate review of NBS results:

History to obtain when called about a positive screen:

Maternal factors that cause false positives or negatives:

Physical Exam Findings and Hemodynamic Assessment

— Vital signs: temperature instability, tachypnea (acidosis from organic acidemia or urea cycle defect), hypotension (CAH adrenal crisis), bradycardia

— Growth parameters: weight loss >10% birth weight, poor weight gain, microcephaly (untreated PKU, congenital CMV)

— Tone: hypotonia (Pompe, SMA, peroxisomal disorders, hypothyroidism), hypertonia/posturing (MSUD encephalopathy)

— Skin: hyperpigmentation of genitalia/areolae → CAH (ACTH excess); eczema → PKU; ichthyosis → Sjögren-Larsson; "blueberry muffin" → not NBS but congenital infection differential

— Eyes: cataracts (galactosemia, congenital rubella), "cherry-red spot" (Tay-Sachs, Niemann-Pick — usually not visible neonatally)

— Genitourinary: ambiguous genitalia, fused labia, clitoromegaly, virilized female → 21-OH deficiency CAH; nonpalpable gonads in apparent male → consider CAH-virilized 46,XX

— Cardiac: murmur, single S2, differential cyanosis → CCHD

— Hepatic: hepatomegaly (galactosemia, tyrosinemia, glycogen storage), conjugated hyperbilirubinemia

— Performed at ≥24 hours of life (earlier increases false positives from transitional circulation)

— Measure right hand (preductal) and either foot (postductal) SpO₂

— Pass: ≥95% in either extremity AND ≤3% absolute difference between RH and foot

— Fail (immediate): any extremity <90%

— Repeat in 1 hour (up to 3 total measurements): 90–94% in both extremities OR >3% difference

— Three failed screens → fail → echocardiogram before discharge, pediatric cardiology consult

CCS pearl: On a CCS case with a "failed CCHD screen," order 4-extremity blood pressures, preductal/postductal SpO₂, CXR, ECG, and echocardiogram, and start prostaglandin E1 infusion empirically if duct-dependent lesion is suspected while awaiting echo — do not wait.

General exam priorities when evaluating an infant with a positive NBS:

System-specific findings tied to specific screened conditions:

Pulse oximetry screen for CCHD — must know the protocol cold:

Diagnostic Workup — Initial Labs and Confirmatory Logic

— State labs report quantitative analyte levels; some values are "borderline" (repeat screen) while others are "presumptive positive" (immediate workup)

— Always examine the infant the same day — do not rely on phone triage alone

— PKU: quantitative plasma amino acids (phenylalanine, tyrosine ratio); BH4 cofactor studies if persistently elevated

— Congenital hypothyroidism: serum TSH and free T4 — do not wait; treat if TSH >40 or FT4 low

— CAH (21-OH deficiency): serum 17-hydroxyprogesterone, electrolytes, glucose, plasma renin, ACTH stimulation if needed

— Galactosemia: erythrocyte GALT enzyme activity and total galactose; stop lactose immediately

— MSUD: plasma amino acids (elevated leucine, isoleucine, valine, alloisoleucine is pathognomonic); urine DNPH

— MCAD: plasma acylcarnitine profile (elevated C8), urine organic acids, ACADM gene sequencing

— SCID: flow cytometry for T-, B-, NK-cell counts; TREC count is the screening assay

— SMA: SMN1 gene deletion testing (homozygous deletion of exon 7 confirms)

— Sickle cell disease: hemoglobin electrophoresis or HPLC confirms FS, FSC, FSA patterns

— CF: sweat chloride test at ≥2 weeks of age and ≥2 kg (≥60 mmol/L = positive); CFTR gene panel

— CBC, CMP (glucose, electrolytes, LFTs, BUN/Cr), ammonia, lactate, blood gas, urinalysis with ketones

— Plasma amino acids, urine organic acids, plasma acylcarnitines — the "metabolic trio"

Step 3 management: Hyperammonemia (>150 µmol/L in a neonate) with respiratory alkalosis = urea cycle defect until proven otherwise — stop protein feeds, give IV dextrose 10% at 1.5× maintenance, and arrange emergent hemodialysis + nitrogen scavengers (sodium phenylacetate/benzoate).

First step when notified of an abnormal NBS: confirm which condition is flagged and how abnormal the value is

Condition-specific initial confirmatory testing (high-yield list):

Always-order baseline labs in a sick or symptomatic infant with positive NBS:

Diagnostic Workup — Advanced and Confirmatory Studies

— Detects >40 disorders of amino acid, organic acid, and fatty acid metabolism in one run

— Reports acylcarnitine and amino acid profiles that flag specific conditions (e.g., elevated C8 → MCAD, elevated C5 → isovaleric acidemia, elevated leucine → MSUD)

— PAH sequencing for PKU, GALT for galactosemia, CFTR for CF, SMN1 for SMA, ACADM for MCAD, HBB for sickle cell

— Carrier identification (e.g., sickle trait FAS on screen) requires parental counseling and confirmatory hemoglobin electrophoresis — not a disease but a reproductive risk

— CCHD: echocardiogram is definitive — defines ductal dependence, arch anatomy, and need for prostaglandin

— Congenital hypothyroidism: thyroid ultrasound or Tc-99m or I-123 scintigraphy distinguishes agenesis, ectopia, dyshormonogenesis (affects counseling, not initial treatment)

— Biliary atresia (NOT on most NBS panels but mimics galactosemia): HIDA scan, liver biopsy, intraoperative cholangiogram — Kasai portoenterostomy by 60 days is critical

— Hearing screen fail: diagnostic ABR by 3 months, intervention by 6 months (the 1-3-6 rule)

— Premature (<32 weeks): repeat at 48–72 h, 7–14 d, and at discharge or 28–36 weeks corrected

— Transfused infants: repeat at 4 months (for hemoglobinopathy detection after donor Hgb clears)

— NPO/TPN at time of first screen: repeat after 24–48 h of enteral feeding

Key distinction: A positive NBS result is a screen, not a diagnosis — you must confirm with disease-specific testing (enzyme assay, genetic test, electrophoresis) before assigning a lifelong diagnosis, but you should begin empiric treatment in parallel for time-sensitive disorders.

Tandem mass spectrometry (MS/MS) is the backbone of the NBS dried blood spot

Molecular/genetic confirmation is increasingly the gold standard:

Imaging and functional studies by condition:

Repeat screening indications:

Whole-genome sequencing is emerging but not yet standard of care for routine NBS — board questions still test the tier 1 confirmatory tests above

Risk Stratification and First-Line Management Logic

— Tier 1 — emergent (call back same day, see immediately, treat empirically): galactosemia, CAH, MSUD, urea cycle defects, organic acidemias, fatty acid oxidation defects (MCAD/VLCAD), SCID

— Tier 2 — urgent (within 24–48 h): congenital hypothyroidism, PKU, biotinidase deficiency, tyrosinemia, sickle cell disease (FS pattern)

— Tier 3 — routine outpatient confirmation (within 1–2 weeks): cystic fibrosis (IRT-only positive), hemoglobinopathy traits, hearing screen fail (must confirm by 3 mo)

— 17-OHP >100 ng/mL on screen → very likely classic CAH → admit, start hydrocortisone, fludrocortisone, IV fluids

— Phenylalanine >600 µmol/L → classic PKU → dietary phe restriction within days of life

— TSH >40 mIU/L → treat with levothyroxine 10–15 µg/kg/day PO immediately; confirm with serum testing same day, do not delay

— Symptomatic infant, poor feeding, lethargy, abnormal tone, ambiguous genitalia

— Family history of affected sibling — pretest probability is high

— Consanguinity raises probability of autosomal recessive disease

— Contact family within 24 h, arrange same-day or next-day visit

— Obtain confirmatory specimen before starting therapy when feasible, but never delay treatment for time-sensitive disorders (CAH, galactosemia, MSUD)

— Refer to subspecialty: metabolic genetics, pediatric endocrinology, pediatric hematology, pediatric immunology, pediatric cardiology — per disorder

Board pearl: Empiric treatment before confirmatory results is the standard of care for galactosemia (stop lactose), CAH (hydrocortisone + saline), and congenital hypothyroidism (levothyroxine) — board questions reward action over waiting.

Triage framework when a state lab calls with a positive NBS:

Severity grading influences urgency:

Risk factors that escalate concern:

Initial action triad for any presumptive positive:

Pharmacotherapy — First-Line Drug and Dietary Regimens

— Levothyroxine 10–15 µg/kg/day PO once daily, crushed tablet in small volume of breast milk/formula/water (do not mix with soy formula, iron, calcium — impair absorption)

— Goal: TSH normalized within 2–4 weeks, free T4 in upper half of normal range

— Recheck TSH/FT4 at 2 and 4 weeks, then every 1–2 months in first 6 months

— Hydrocortisone 10–15 mg/m²/day PO divided TID (mineralocorticoid + glucocorticoid replacement)

— Fludrocortisone 0.1–0.2 mg/day PO for salt-wasters

— Sodium chloride supplementation 1–2 g/day in infancy

— Stress-dose steroids (3× baseline) for fever, illness, surgery

— Phenylalanine-restricted formula (Phenex-1, Lofenalac) — maintain plasma phe 120–360 µmol/L

— Sapropterin (Kuvan) for BH4-responsive variants

— Lifelong dietary management; "diet for life" — relaxation in adulthood causes cognitive decline and is contraindicated in pregnancy (maternal PKU syndrome)

Step 3 management: Always give the first dose in the office or on admission when starting levothyroxine or hydrocortisone — never send the family home to "fill it tomorrow."

Congenital hypothyroidism:

Congenital adrenal hyperplasia (21-OH deficiency):

Phenylketonuria:

Galactosemia: soy-based or elemental formula (no lactose); lifelong dairy restriction

MSUD: branched-chain amino acid-restricted formula; emergency protocol with high-dextrose IV during illness to prevent catabolism

MCAD: avoid fasting >8 h in infancy; emergency letter for ED visits; IV dextrose during illness; no specific drug

Sickle cell disease: penicillin VK 125 mg PO BID starting by 2 months (prophylaxis through age 5); pneumococcal vaccines per schedule; folic acid 1 mg/day; hydroxyurea by 9 months per NHLBI

SCID: strict isolation, no live vaccines (no rotavirus, BCG), IVIG, PJP prophylaxis (TMP-SMX) → hematopoietic stem cell transplant by 3.5 months dramatically improves survival

SMA: nusinersen, onasemnogene abeparvovec (Zolgensma), or risdiplam — earlier treatment = better motor outcomes

Procedures, Specialty Referrals, and Definitive Interventions

— Definitive cure; survival >90% if transplanted by 3.5 months vs. ~70% after

— HLA-matched sibling preferred; haploidentical or matched unrelated donor otherwise

— Pre-transplant: isolation, IVIG, TMP-SMX prophylaxis, irradiated/CMV-negative blood products only, no live vaccines

— Onasemnogene abeparvovec (Zolgensma): single-dose AAV9 gene therapy for SMA <2 years; monitor LFTs and platelets

— Elexacaftor/tezacaftor/ivacaftor (Trikafta): CFTR modulator for cystic fibrosis ≥2 years with at least one F508del allele

— Crysvita, Strensiq, etc.: enzyme replacement for emerging NBS conditions (Pompe, MPS-I, X-ALD)

— CCHD: catheter-based or surgical repair depending on lesion (Norwood for HLHS, arterial switch for TGA, BT shunt for ductal-dependent pulmonary flow)

— Biliary atresia (clinical, not on NBS but mimics galactosemia): Kasai hepatoportoenterostomy ideally by 45–60 days for best outcome

— Cochlear implantation for profound bilateral SNHL not responsive to hearing aids

— Metabolic geneticist: any amino acidopathy, organic acidemia, fatty acid oxidation disorder, urea cycle defect — same-day phone consult

— Pediatric endocrinology: CAH, congenital hypothyroidism

— Pediatric hematology: sickle cell disease — first visit by 2 months

— Pediatric immunology: SCID, agammaglobulinemia — same-day

— Pediatric cardiology: failed CCHD screen — before discharge

— Audiology + ENT + early intervention: failed hearing screen by 3 months, intervention by 6 months

— Pulmonology + CF center: confirmed CF within 1–2 weeks of diagnosis

CCS pearl: On a CCS case with confirmed SCID, your standing orders are: place in protective isolation, IVIG infusion, TMP-SMX prophylaxis, irradiated CMV-negative leukoreduced blood products if needed, hold all live vaccines, urgent immunology + BMT consult, and counsel parents on transplant evaluation.

Hematopoietic stem cell transplant (HSCT) for SCID:

Gene therapy and disease-modifying agents (newer, board-relevant):

Surgical interventions:

Specialty referral cadence (Step 3 favorite):

Special Populations — Preterm, Low Birth Weight, and Sick Neonates

— Standard protocol: screen at 24–48 h, repeat at 14 days or at 28–36 weeks corrected GA, then again at NICU discharge

— Persistent borderline TSH elevation is common in preemies — delayed TSH rise can be missed on the initial screen

— RBC transfusion before NBS can mask hemoglobinopathies (donor Hgb dominates electrophoresis)

— Repeat screen at 4 months for hemoglobinopathy detection after donor cells clear

— Document transfusion on the screening card

— Phenylalanine, methionine, and other amino acids may be falsely low because the infant has not been protein-fed

— Repeat screen 24–48 h after starting enteral feeds

— Antenatal betamethasone → suppressed fetal 17-OHP → false-negative CAH screen → maintain clinical vigilance for salt-wasting at 1–2 weeks

— Maternal hyperthyroidism with thionamides → transient neonatal hypothyroidism

— Maternal B12 deficiency (vegan diet, gastric bypass) → elevated propionylcarnitine in infant → mimics propionic acidemia → check maternal B12 level

— Maternal vitamin D deficiency → not screened but check if infant has rickets later

— Sick neonates with multiorgan failure can have elevated tyrosine, methionine, or phenylalanine from liver dysfunction — repeat after recovery

— Renal failure can elevate citrulline and other amino acids — interpret with caution

— Each infant requires separate specimen

— Monozygotic twin with positive screen → screen co-twin

Board pearl: A 34-week preemie with a negative initial CAH screen who develops vomiting, hyponatremia, and hyperkalemia at day 10 likely has antenatal-steroid-suppressed 17-OHP — repeat 17-OHP and treat empirically; do not be falsely reassured by the negative screen.

Premature infants have higher false-positive and false-negative rates on NBS due to immature enzyme systems, parenteral nutrition, and transfusions

Transfused infants:

NPO or TPN-dependent infants:

Maternal influences:

Renal or hepatic dysfunction in neonates:

Twins and conjoined twins:

Special Populations — Adopted, Out-of-Hospital Births, and Refugee Infants

— Parents may decline NBS or be unaware of the requirement

— All 50 states mandate offering NBS; most allow religious exemption but only a few allow philosophical exemption

— Primary care provider at first newborn visit must verify NBS was performed and order it if missed — collect specimen ASAP, ideally by 7 days

— Many countries have limited or no NBS — assume not done unless documented

— Order expanded metabolic panel, hemoglobin electrophoresis, TSH/FT4, hearing/vision screen, HIV, hepatitis B/C, syphilis, TB, stool O&P at first U.S. visit

— Consider repeat NBS if age <6 months and country of origin has incomplete screening

— Same approach as international adoptees; coordinate with refugee health clinic

— Pay attention to hemoglobinopathies (sickle cell from sub-Saharan Africa, β-thalassemia from Mediterranean/Southeast Asia, α-thalassemia from East Asia)

— G6PD deficiency common in Mediterranean, African, and Southeast Asian populations — counsel on fava bean and oxidant drug avoidance (though G6PD is not universally on U.S. NBS panels)

— Document conversation thoroughly; involve social work and ethics if infant is symptomatic

— In most states, NBS for life-threatening conditions can be performed over parental objection under child welfare statutes if the infant is symptomatic — varies by state

— Women with PKU who are not on phe-restricted diet during pregnancy have infants with microcephaly, congenital heart disease, intellectual disability — infant does not have PKU, NBS will be negative

— Prevent by pre-conception counseling: maintain maternal phe 120–360 µmol/L from before conception through delivery

Step 3 management: At every newborn visit (2 weeks, 1 month, 2 months), confirm NBS results are in the chart — missing or pending results are a leading source of medical-legal exposure and patient safety events.

Home births and birthing center deliveries:

Adopted and internationally adopted children:

Refugee and immigrant infants:

Religious or philosophical refusal:

Maternal PKU syndrome:

Complications and Adverse Outcomes of Missed or Delayed Diagnosis

— Progressive intellectual disability (IQ drops ~50 points by age 1 if untreated), seizures, eczema, "mousy" odor, hypopigmentation

— Outcomes are excellent if diet started <10 days of life

— Cretinism: severe intellectual disability, short stature, coarse facies, umbilical hernia, hypotonia, prolonged jaundice

— Each week of delayed treatment = measurable IQ loss; treatment by 2 weeks preserves near-normal cognition

— Salt-wasting crisis at 1–3 weeks: vomiting, dehydration, hyponatremia, hyperkalemia, shock, death if not treated with hydrocortisone + saline

— Virilization of 46,XX infants → genital ambiguity, psychosocial impact

— E. coli sepsis (specific association!), cataracts, hepatic failure, intellectual disability, ovarian failure (long-term)

— Sudden infant death during first fasting illness; hypoketotic hypoglycemia, hyperammonemia, Reye-like syndrome

— Mortality ~25% at first decompensation; preventable with avoiding fasting + emergency dextrose

— Severe opportunistic infections (PJP, CMV, rotavirus from live vaccine), failure to thrive, death by 1–2 years without HSCT

— Death or permanent ventilator dependence by age 2 without disease-modifying therapy

— Cardiovascular collapse at home when ductus arteriosus closes (typical age 1–2 weeks); leading cause of preventable infant death from cardiac causes

— Language delay, academic failure; the 1-3-6 rule (screen by 1 month, diagnose by 3 months, intervention by 6 months) preserves language acquisition

Board pearl: A 10-day-old with vomiting, lethargy, hyponatremia (Na 120), hyperkalemia (K 6.5), and hypoglycemia is CAH salt-wasting crisis — give IV normal saline bolus + D10, IV hydrocortisone 25 mg, and recheck 17-OHP before discharge; this is a classic NBS-related Step 3 emergency.

Untreated PKU:

Untreated congenital hypothyroidism:

Untreated CAH:

Untreated galactosemia:

Untreated MCAD:

Untreated SCID:

Untreated SMA type 1:

Missed CCHD:

Delayed hearing diagnosis:

When to Escalate Care — ICU, Consult, and Inpatient Triage

— Symptomatic infant with metabolic acidosis, hyperammonemia, hypoglycemia, or altered mental status

— Failed CCHD screen with ductal-dependent lesion → start PGE1 0.05–0.1 µg/kg/min in transport

— Presumptive CAH salt-wasting crisis: hypotension, hyponatremia, hyperkalemia

— Presumptive galactosemia with sepsis: blood culture, broad-spectrum antibiotics covering E. coli + soy formula

— Hyperammonemia >150 µmol/L: stop protein, IV dextrose, nitrogen scavengers, prepare for hemodialysis (most effective rapid ammonia clearance in neonates)

— SCID with infection: PICU-level isolation, IVIG, broad antimicrobials

— Asymptomatic infant with confirmed PKU, MCAD, hypothyroidism, biotinidase deficiency — start therapy, close follow-up in 2–7 days

— Confirmed sickle cell — initiate penicillin prophylaxis, education, hematology consult within 1 week

— Metabolic genetics: any amino acid, organic acid, fatty acid oxidation, or urea cycle disorder

— Pediatric endocrinology: CAH, congenital hypothyroidism

— Pediatric cardiology: failed CCHD screen

— Pediatric hematology: hemoglobinopathies

— Pediatric immunology + BMT: SCID

— Pediatric pulmonology + CF center: confirmed CF

— Audiology + ENT: failed hearing screen

— Neurology + early intervention: SMA, leukodystrophies (Krabbe, X-ALD)

— Social work + nutrition: dietary disorders requiring specialized formulas and emergency letters

— Need for hemodialysis (neonatal hyperammonemia)

— Cardiac surgery

— HSCT for SCID

— Liver transplant consideration (advanced tyrosinemia, urea cycle defects)

CCS pearl: When a CCS case opens with a positive NBS for an amino acid or organic acid disorder, your first three orders should be: (1) NPO, (2) IV D10 at 1.5× maintenance, (3) STAT plasma ammonia, lactate, amino acids, urine organic acids, and acylcarnitines — then call metabolic genetics.

Immediate admission to NICU/PICU is required for:

Same-day urgent outpatient or short-stay observation:

Subspecialty consultations to order on Step 3 CCS:

Transfer to tertiary care for:

Key Differentials — Other Causes Within the Same Category

— Urea cycle defects: OTC (X-linked, most common), CPS1, ASS (citrullinemia), ASL (argininosuccinic aciduria), arginase deficiency

— Organic acidemias: propionic, methylmalonic, isovaleric — distinguish by anion gap acidosis with ketosis (urea cycle defects classically have respiratory alkalosis, no acidosis, no ketosis)

— Fatty acid oxidation defects: hypoketotic hypoglycemia + hyperammonemia

— Transient hyperammonemia of the newborn (THAN): usually preterm, resolves with supportive care

— Fatty acid oxidation defects (MCAD, VLCAD, LCHAD): hypoketotic

— Glycogen storage diseases: hepatomegaly + ketotic hypoglycemia

— Hyperinsulinism: not on NBS; persistent hypoglycemia requiring high glucose infusion rate (>8 mg/kg/min)

— Panhypopituitarism: midline defects, micropenis, low cortisol/GH

— Galactosemia: conjugated, with hepatomegaly, E. coli sepsis

— Tyrosinemia type 1: cabbage odor, succinylacetone in urine (now on most NBS panels)

— Congenital hypothyroidism: prolonged unconjugated jaundice

— Biliary atresia (not on NBS but always on differential): conjugated, acholic stools — Kasai by 60 days

— SMA (anterior horn): areflexia, tongue fasciculations, alert face

— Pompe disease (GAA deficiency): cardiomegaly, hepatomegaly, glycogen accumulation — now on RUSP

— Congenital hypothyroidism: macroglossia, umbilical hernia

— Peroxisomal disorders (Zellweger): dysmorphic features, seizures — X-ALD is on NBS

Key distinction: Organic acidemia = high anion gap metabolic acidosis + ketosis + hyperammonemia; urea cycle defect = respiratory alkalosis + hyperammonemia + NO acidosis + NO ketosis — this distinction drives initial empiric management.

Causes of neonatal hyperammonemia (the "metabolic encephalopathy" differential):

Causes of neonatal hypoglycemia with positive NBS to consider:

Causes of neonatal jaundice with positive NBS:

Causes of hypotonia with positive NBS:

Key Differentials — Conditions That Mimic NBS Disorders

— Always obtain blood/urine/CSF cultures and start empiric ampicillin + gentamicin (or cefotaxime) in a sick neonate, even while metabolic workup proceeds

— Galactosemia famously presents with E. coli sepsis — treat both simultaneously

— Lethargy, seizures, hypotonia in first 24 h — distinguish by perinatal history, cord gas, Apgar scores

— Lactate may be elevated in both HIE and metabolic disease

— CMV, toxoplasmosis, rubella, syphilis — present with hepatosplenomegaly, thrombocytopenia, jaundice

— NBS does not routinely screen for these (CMV being added in some states for hearing loss workup)

— Hearing loss differential: congenital CMV is the most common non-genetic cause of SNHL — consider CMV PCR on a saved NBS card or saliva PCR within 3 weeks of birth

— 3–6-week-old with projectile vomiting, hypochloremic hypokalemic metabolic alkalosis

— Can be confused with CAH salt-wasting (CAH has hyperkalemia and acidosis — opposite electrolyte pattern)

— Vomiting, diarrhea, weight loss — distinguish from galactosemia (no liver dysfunction, normal NBS)

— Mitochondrial disorders, glycogen storage disease type 1 (von Gierke), Wilson disease, lysosomal storage disorders not yet added (Niemann-Pick, Gaucher in some states)

— Maintain high clinical suspicion despite "normal NBS"

— TPN can elevate amino acids

— Maternal B12 deficiency → false positive for propionic acidemia

— Premature TSH rise can be missed initially → false negative

Board pearl: A 2-week-old with projectile vomiting, hypochloremic hypokalemic metabolic alkalosis, and a palpable "olive" is pyloric stenosis, not CAH — CAH has hyperkalemia and acidosis. The electrolyte pattern is the discriminator.

Sepsis mimics nearly every metabolic emergency in a neonate:

Hypoxic-ischemic encephalopathy (HIE):

Congenital infections (TORCH):

Pyloric stenosis:

Cow's milk protein allergy / food protein-induced enterocolitis:

Inborn errors not on NBS panel:

False-positive screens:

Secondary Prevention, Long-Term Plans, and Lifelong Management

— Lifelong phe-restricted diet; phe goal 120–360 µmol/L through childhood; some relaxation in adulthood but still monitored

— Maternal PKU: women must achieve phe <360 µmol/L before conception through delivery to prevent maternal PKU embryopathy

— Lifelong levothyroxine; trial off therapy after age 3 for some transient cases under endocrine guidance

— Annual TSH/FT4, growth, development monitoring

— Lifelong glucocorticoid + mineralocorticoid; medical alert bracelet, emergency hydrocortisone IM injection for families to keep at home

— Stress dose for illness, surgery; transition to adult endocrinology in adolescence

— Monitor growth velocity, bone age, virilization, fertility

— Penicillin VK 125 mg BID through age 3, then 250 mg BID through age 5

— Pneumococcal vaccines (PCV13/PCV15 series + PPSV23 at age 2 and 5), meningococcal, annual influenza

— Hydroxyurea starting at 9 months per NHLBI 2014 guidelines

— Annual transcranial Doppler ages 2–16 to screen for stroke risk (TCD >200 cm/s → chronic transfusion)

— Folic acid 1 mg/day

— CF center care, pancreatic enzyme replacement, fat-soluble vitamins (ADEK), airway clearance, dornase alfa, CFTR modulators (Trikafta if eligible)

— Avoid fasting >8 h in infants, >12 h in children; emergency letter for ED

— IV dextrose during illness; cornstarch at bedtime in older children

— Ongoing neurology, PT/OT, respiratory care, nutrition

Step 3 management: Every child with an NBS-detected chronic disease needs a medical home + subspecialty team + written emergency action plan + medical alert ID + insurance/Medicaid coordination + early intervention referral — the longitudinal management triad is a Step 3 favorite.

PKU:

Congenital hypothyroidism:

CAH:

Sickle cell disease:

Cystic fibrosis:

MCAD / fatty acid oxidation defects:

SMA after disease-modifying therapy:

Galactosemia: lifelong lactose-free diet; monitor for cataracts, ovarian function, speech/cognitive delay

Follow-Up, Monitoring Parameters, and Family Counseling

— Confirmatory testing within 24–72 h of presumptive positive

— Subspecialty visit within 1 week of confirmation

— Genetic counseling for the family — recurrence risk for autosomal recessive disorders is 25% per pregnancy

— PKU: phe levels weekly in infancy, then monthly; quarterly developmental assessment

— Congenital hypothyroidism: TSH/FT4 at 2 and 4 weeks, then every 1–2 months for first 6 months, every 3–4 months until age 3, then every 6–12 months

— CAH: 17-OHP, androstenedione, electrolytes, plasma renin every 3 months in infancy; growth, bone age annually

— Sickle cell: hematology every 3 months in infancy, annual TCD ages 2–16, retinal exam from age 10

— CF: CF center visits every 1–3 months, pulmonary function from age 5–6, sweat chloride, microbiology

— MCAD: metabolic clinic every 6–12 months; acute illness management plan

— Failed screen → diagnostic ABR by 3 months

— Confirmed hearing loss → early intervention by 6 months

— Hearing aids, cochlear implant evaluation, sign language as appropriate

— Inform family that infant is a carrier, not affected

— Recommend parental hemoglobin electrophoresis for reproductive planning

— Genetic counseling for future pregnancies

— Use plain language; "your baby's test showed a possible problem we need to confirm"

— Avoid the word "positive" alone — "presumptive positive" or "needs confirmatory testing"

— Reassurance that early treatment prevents most adverse outcomes

— Written instructions, follow-up appointment scheduled before family leaves the office

Board pearl: A carrier (trait) result on NBS is not a diagnosis but is a reproductive risk — parents should be offered carrier testing themselves and genetic counseling before future pregnancies.

Standard follow-up cadence after positive NBS (general principles):

Condition-specific monitoring:

Hearing screen follow-up (1-3-6 rule):

Carrier results (e.g., FAS sickle trait):

Counseling principles:

Ethical, Legal, and Patient Safety Considerations

— All 50 states mandate NBS; religious exemption is allowed in most states, philosophical exemption in only a few

— If parents refuse, document extensively, involve ethics committee and social work, and in cases of symptomatic infants with treatable conditions, state child welfare laws may permit testing/treatment over objection

— Informed consent for the screening itself is not universally required — opt-out structure varies by state

— Many states retain NBS cards for years; some use them for research (de-identified)

— Privacy concerns: parents have the right to know storage policies; some states allow request for destruction

— Recent legal challenges (e.g., Texas, Michigan) have shaped state retention rules

— Confirmed cases of certain conditions (e.g., hemoglobinopathies in some states) must be reported to state public health surveillance

— This is public health reporting, not a violation of HIPAA

— NBS results may not be available before hospital discharge — discharge summary must include statement that results are pending

— Primary care provider must verify NBS results at first newborn visit (2–3 days post-discharge)

— A pending or missing NBS result is a leading patient safety event — implement EMR alerts and closed-loop reporting

— Home births: nurse-midwife or PCP is responsible for ensuring NBS is performed

— Carrier status detected (e.g., sickle trait, CF carrier) → must be disclosed to parents

— Misattributed paternity sometimes revealed by genetic testing → handle with sensitivity; standard practice is to disclose only to the mother

— State panels vary; infants born in states with fewer conditions miss diagnoses available in other states

— RUSP harmonization is ongoing; advocacy for universal panels is part of value-based pediatrics

Step 3 management: When discharging a newborn before NBS results return, document that results are pending, schedule the 2–3 day follow-up visit before discharge, and ensure the receiving PCP has a mechanism to retrieve and act on results — failure to follow up on a pending NBS is the most common malpractice scenario in this domain.

Mandatory screening laws and parental refusal:

Residual dried blood spot storage:

Mandatory reporting obligations:

Transition-of-care risks (Step 3 favorite):

Disclosure of incidental findings:

Equity and access:

High-Yield Associations and Rapid-Fire Clinical Facts

Board pearl: Memorize the smell associations — they appear on every NBS question: mousy = PKU, maple syrup = MSUD, sweaty feet = isovaleric, cabbage = tyrosinemia, fish = trimethylaminuria.

Galactosemia + E. coli sepsis = pathognomonic association; stop lactose immediately

PKU + "mousy" body odor + eczema + hypopigmented hair = untreated phenylketonuria

MSUD + maple syrup odor of cerumen and urine = branched-chain ketoaciduria; alloisoleucine is pathognomonic

Isovaleric acidemia + "sweaty feet" odor = elevated C5 acylcarnitine

CAH 21-OH deficiency + salt-wasting + ambiguous genitalia in 46,XX = elevated 17-OHP

MCAD + hypoketotic hypoglycemia after fasting = elevated C8 acylcarnitine

Urea cycle defect + respiratory alkalosis + hyperammonemia + NO acidosis = classically OTC deficiency (X-linked recessive)

SCID + lymphopenia (ALC <2500) + absent thymic shadow on CXR = need TREC confirmation, no live vaccines, HSCT by 3.5 months

SMA + tongue fasciculations + areflexia + alert face = homozygous SMN1 deletion

Sickle cell + dactylitis (hand-foot syndrome) at 6 months = first manifestation in many infants

Congenital hypothyroidism + prolonged jaundice + umbilical hernia + macroglossia + constipation = treat with levothyroxine before confirmatory imaging

CCHD screen: fail = SpO₂ <90% in any limb, OR 90–94% in both limbs on 3 measurements, OR >3% difference between RH and foot

1-3-6 rule for hearing: screen by 1 month, diagnose by 3 months, intervention by 6 months

Cystic fibrosis NBS: IRT → if elevated, reflex to CFTR mutation panel → confirmatory sweat chloride (≥60 mmol/L positive, 30–59 intermediate, <30 normal)

Biotinidase deficiency: alopecia, seborrheic dermatitis, seizures, lactic acidosis — treat with biotin 5–20 mg/day PO; excellent prognosis with early treatment

Tyrosinemia type 1: cabbage odor, liver failure, renal Fanconi syndrome — treat with nitisinone (NTBC) + phe/tyr-restricted diet

X-linked adrenoleukodystrophy (X-ALD): now on RUSP; very long-chain fatty acids elevated; HSCT can halt progression if performed early

Board Question Stem Patterns

— "A 5-day-old infant has a state newborn screen reporting elevated 17-hydroxyprogesterone. The mother says the baby is feeding well. What is the next best step?"

— Answer: Examine the infant the same day, draw confirmatory 17-OHP and electrolytes, consult pediatric endocrinology — do not wait

— "A 10-day-old breastfed infant presents with vomiting, lethargy, jaundice, and E. coli bacteremia. What is the most likely underlying diagnosis?"

— Answer: Galactosemia — stop lactose, switch to soy formula, confirm with GALT enzyme activity

— "A 3-day-old has lethargy, tachypnea, ammonia 450, pH 7.50 with respiratory alkalosis, no ketones in urine. What is the next step?"

— Answer: Urea cycle defect — stop protein, IV D10, sodium phenylacetate/benzoate, prepare for hemodialysis

— "At 26 hours of life, an infant has SpO₂ 88% in the right hand and 86% in the foot. What is the next step?"

— Answer: Failed screen — order echocardiogram before discharge; if cyanotic and concern for ductal-dependent lesion, start PGE1

— "A 14-day-old presents with vomiting, weight loss, Na 122, K 6.4, glucose 45. NBS results pending. Most likely diagnosis?"

— Answer: CAH salt-wasting crisis — IV NS bolus + D10, IV hydrocortisone 25 mg, draw 17-OHP before steroids

— "A 32-week preemie had a negative NBS at day 2. Now at 3 weeks she has feeding intolerance and Na 128. What was the testing pitfall?"

— Answer: Antenatal steroids suppress 17-OHP, causing false-negative CAH screen; repeat 17-OHP now

— "An infant's NBS shows hemoglobin pattern FAS. What do you tell the parents?"

— Answer: Sickle cell trait (carrier), not disease; confirm with hemoglobin electrophoresis; recommend parental testing and genetic counseling

— "An infant born at home presents at 10 days for first visit. No NBS performed. Next step?"

— Answer: Collect NBS dried blood spot today; do not delay

Step 3 management: The right answer is almost always "see the baby today, draw confirmatory tests, start empiric treatment for time-sensitive disorders, and consult the appropriate subspecialist" — never "repeat the screen and call me in a week."

Stem pattern 1 — The Asymptomatic Phone Call:

Stem pattern 2 — The Crashing Neonate:

Stem pattern 3 — The Hyperammonemia Differential:

Stem pattern 4 — The Failed CCHD Screen:

Stem pattern 5 — The Salt-Waster:

Stem pattern 6 — The Preterm Pitfall:

Stem pattern 7 — The Carrier Result:

Stem pattern 8 — The Missing Screen:

One-Line Recap

Newborn screening is a state-mandated, time-sensitive public health program in which a presumptive positive result demands same-day clinical evaluation, disease-specific confirmatory testing, and — for time-critical disorders like CAH, galactosemia, MSUD, urea cycle defects, and SCID — empiric treatment initiated before confirmation, because early intervention prevents catastrophic and irreversible neurodevelopmental, metabolic, and infectious sequelae.

Board pearl: When in doubt on the exam, see the baby today, treat empirically for time-sensitive disorders, confirm in parallel, and consult the subspecialist — that combination is the right answer on virtually every NBS question.

Three pillars of NBS: dried blood spot (38 RUSP core conditions), pulse oximetry for CCHD at ≥24 h (fail = <90% any limb, or 90–94% bilateral, or >3% RH-foot difference on three measurements), and hearing screen (1-3-6 rule: screen by 1 mo, diagnose by 3 mo, intervention by 6 mo)

The Big Six emergencies triggered by a positive NBS — recognize and treat empirically: CAH (hydrocortisone + saline), galactosemia (stop lactose), MSUD (BCAA-restricted formula + dialysis if severe), urea cycle defect (stop protein + IV D10 + dialysis + scavengers), MCAD (avoid fasting + IV dextrose), SCID (isolation + IVIG + no live vaccines + HSCT by 3.5 months)

High-yield smell, electrolyte, and lab pearls: mousy = PKU, maple syrup = MSUD, sweaty feet = isovaleric, cabbage = tyrosinemia; respiratory alkalosis + hyperammonemia + no acidosis = urea cycle; anion gap acidosis + ketosis + hyperammonemia = organic acidemia; hyponatremia + hyperkalemia + virilization = CAH; conjugated jaundice + E. coli sepsis = galactosemia

Transition-of-care safety: at every newborn visit, confirm NBS results are in the chart, document pending results in discharge paperwork, and ensure closed-loop follow-up — a missed or unaddressed positive screen is the leading malpractice scenario in this domain, and PCPs at the 2–3 day visit are the safety net