When should thyroid screening be performed in children, including newborns and those with risk factors?

Thyroid Screening in Children

All newborns should be screened for congenital hypothyroidism within 24-48 hours of birth using either TSH or T4 measurement, as this is one of the most critical preventive medicine interventions to prevent irreversible mental retardation. 1, 2

Newborn Screening (Universal)

Timing and Method

• Blood spot screening should be performed after 24 hours of age to minimize false positives from the physiological TSH surge that occurs in the first 1-2 days after birth 1
• Two primary strategies exist: primary TSH screening (more specific, detects primary hypothyroidism) or primary T4 with follow-up TSH (more sensitive, also detects central hypothyroidism but higher false positive rate) 3
• TSH screening is more specific and cost-effective, though it will miss rare cases of central hypothyroidism 3, 1

Critical Timing Considerations

• Therapy must be initiated within 2 weeks of age to normalize cognitive development 2
• Unrecognized congenital hypothyroidism leads to irreversible mental retardation, making this screening absolutely essential 1, 2

Special Populations Requiring Second Screening

• Very low birth weight infants require repeat testing even with normal initial TSH because delayed TSH elevation is common in this population 4
• Premature infants should have TSH and free T4 rechecked, as most cases requiring treatment (22/30 in one study) exhibited delayed TSH elevation missed by initial screening 4
• Many U.S. programs do not use age-adjusted TSH cutoffs after 48 hours, potentially missing mild persistent hypothyroidism in infants tested at 1 week to 1 month of age 5

High-Risk Children Requiring Periodic Screening

Children with Type 1 Diabetes

• Screen TSH every 1-2 years due to 17-30% risk of developing autoimmune thyroid disease 6, 7
• Children with positive thyroid autoantibodies require more frequent monitoring due to higher progression risk 7

Children with Down Syndrome

• Screen TSH and free T4 every 1-2 years due to markedly increased risk of thyroid abnormalities 8, 7
• Evaluating hypothyroidism symptoms is particularly difficult in Down syndrome because features like slow speech, thick tongue, and slow mentation overlap with Down syndrome itself 8

Children with 22q11.2 Deletion Syndrome

• Monitor TSH and free T4 every 1-2 years per American College of Medical Genetics and Genomics recommendations 6

Symptomatic Children Requiring Immediate Evaluation

When to Test Outside Routine Screening

• Any child with growth abnormalities, developmental delays, unexplained fatigue, or behavioral changes should have TSH and free T4 measured 7
• Children with speech delay or developmental concerns warrant thyroid function evaluation 7
• Never rely solely on normal newborn screening results if clinical symptoms suggest hypothyroidism, as hypothyroidism can be acquired after the newborn period 2

Diagnostic Approach for Abnormal Results

• Measure both TSH and free T4 to distinguish overt hypothyroidism (elevated TSH, low free T4) from subclinical hypothyroidism (elevated TSH, normal free T4) 7
• Check thyroid peroxidase (TPO) antibodies and thyroglobulin antibodies to assess for autoimmune thyroid disease 7
• Repeat abnormal values before making treatment decisions, as TSH can vary by up to 50% day-to-day 7

Critical Pitfalls to Avoid

• Do not assume normal newborn screening excludes hypothyroidism if clinical symptoms develop later—acquired hypothyroidism occurs after the newborn period 2
• Do not use adult TSH reference ranges for children—pediatric ranges differ by age, with values above 6.5 mU/L generally considered elevated 7
• Do not overlook central hypothyroidism (low TSH with low free T4), which requires different management and is missed by TSH-only screening 7, 2
• In very low birth weight infants, do not rule out hypothyroidism based solely on normal initial screening—delayed TSH elevation is common and requires repeat testing 4