At what age intervals is blood work typically required for infants with and without underlying medical conditions?

Blood Work Timing in Infants

For healthy term infants without underlying conditions, routine blood work is not indicated beyond newborn screening and jaundice assessment in the first days of life, while infants with specific medical conditions require targeted surveillance based on their diagnosis. 1, 2

Healthy Term Infants (≥35 weeks gestation)

First 24-72 Hours

• Bilirubin screening (transcutaneous or serum) is mandatory for all jaundiced infants within the first 24 hours after birth 1
• Repeat bilirubin measurements depend on the initial zone classification and clinical evolution, not a fixed schedule 1
• No routine CBC or other blood work is recommended for asymptomatic healthy infants 2

Beyond First Week

• At 3 weeks: If jaundice persists or infant appears sick, measure total and direct/conjugated bilirubin to identify cholestasis, and verify newborn thyroid and galactosemia screening results 1
• No routine surveillance blood work is indicated for healthy infants without risk factors 2

Critical Pitfall

Visual estimation of jaundice severity is unreliable, particularly in darkly pigmented infants—always obtain objective bilirubin measurement if jaundice appears excessive 1

Preterm and Critically Ill Infants

Extremely Preterm (<28 weeks)

• Blood sampling frequency is highest during the first week of life, averaging 0.7 samples per day per infant 3
• No fixed schedule exists—sampling is driven by clinical status, cardiopulmonary support requirements, and specific complications 3
• Mean blood loss from phlebotomy reaches 13.6 mL/kg in the first 4 weeks, with 70% of extremely preterm infants requiring transfusion 3

Monitoring Principle

The American Society of Hematology emphasizes using age-specific, analyzer-specific, and reagent-specific reference ranges when interpreting pediatric results, as adult ranges misclassify up to 30% of normal children 2

Infants with Specific Conditions

Genetic Predisposition Syndromes

Beckwith-Wiedemann Syndrome/Isolated Hemihyperplasia:

• AFP and abdominal ultrasound every 3 months from birth through 4th birthday for hepatoblastoma screening 1
• AFP values must be interpreted using BWS-specific reference ranges (elevated compared to general pediatric values) and trend over time 1
• If AFP rises >50-100 ng/mL, repeat in 6 weeks; if >1000 ng/mL, proceed directly to MRI 1

Noonan Syndrome/CBL Syndrome:

• Physical examination every 3 months through age 1 year, then at well-child visits until age 5 years 1
• CBC only if symptomatic (hepatosplenomegaly, clinical concern for leukemia)—no routine blood work for asymptomatic children 1
• Consult hematology immediately if abnormal blood work detected 1

Ataxia-Telangiectasia:

• No routine annual blood work recommended for early detection of hematologic malignancies 1
• Unlike myelodysplastic syndromes, there is no evidence supporting routine CBC for detecting ALL or lymphoma in asymptomatic patients 1
• Prompt evaluation required only when signs/symptoms suggest malignancy 1

Congenital Toxoplasmosis

Confirmed infection:

• Serologic testing every 3 months for first 2 years of life 1
• Every 6 months during third year 1
• Yearly thereafter indefinitely 1

Unlikely infection:

• Serologic follow-up every 2 months until Toxoplasma IgG antibodies become undetectable 1

Age-Specific Interpretation Considerations

Hemoglobin Reference Ranges

The American Academy of Pediatrics mandates using standardized age groupings (neonates, 1 month-1 year, 1-5 years, 6-10 years, 11-16 years) that reflect statistically different physiological states 2

Hemoglobin Electrophoresis

For thalassemia diagnosis, hemoglobin patterns stabilize by 6 months of age, making this the preferred time for definitive diagnosis—never interpret results in infants <6 months using adult reference ranges 4

When to Obtain Urgent Blood Work

Immediate Indications

• Jaundice in first 24 hours of life 1
• Jaundice persisting at/beyond 3 weeks 1
• Sick-appearing infant at any age 1
• Hepatosplenomegaly on examination 1
• Clinical signs of leukemia/lymphoma 1
• Rapid bilirubin rise crossing percentiles unexplained by history 1

Hematology Referral Triggers

The American Society of Hematology recommends immediate consultation for: severe cytopenias (Grade 3-4), multiple cell line abnormalities, presence of blasts or dysplastic changes, persistent unexplained cytopenias, or suspected hematologic malignancy 2