Diagnostic Criteria for Congenital Hypothyroidism
The diagnosis of congenital hypothyroidism requires elevated TSH levels (>20 mIU/L in serum) with low free T4 or total T4 levels, confirmed through appropriate laboratory testing following an abnormal newborn screening result. 1, 2
Newborn Screening
- All newborns should undergo screening for congenital hypothyroidism 2
- Screening methods include:
- Optimal timing: 48-72 hours after birth to avoid false positives from physiological TSH surge 1, 3
- For preterm and low birth weight infants: Screen at 48-72 hours of age 1
- For sick babies: Screen by 7 days of age at the latest 1
Recall Criteria and Confirmatory Testing
- Recall for confirmatory testing if:
- For screen TSH >40 mIU/L: Immediate confirmatory venous T4/FT4 and TSH 1
- For milder TSH elevations: Repeat screening TSH at 7-10 days of age 1
Diagnostic Confirmation Thresholds
- Venous confirmatory TSH >20 mIU/L before age 2 weeks 1
- Venous confirmatory TSH >10 mIU/L after age 2 weeks 1
- Low T4 (<10 μg/dL) or FT4 (<1.17 ng/dL) 1
Clinical Presentation
Despite screening programs, physicians should remain vigilant for clinical signs of congenital hypothyroidism, which may include:
- Decreased activity and increased sleep
- Feeding difficulties
- Constipation
- Prolonged jaundice
- Myxedematous facies
- Large fontanels
- Macroglossia
- Distended abdomen with umbilical hernia
- Hypotonia
- Hypothermia 4, 2
Additional Diagnostic Workup
After biochemical confirmation, but without delaying treatment:
Special Considerations
- Transient congenital hypothyroidism: More common in preterm infants and areas with iodine deficiency; requires re-evaluation at age 3 years 4, 1
- Central (secondary) hypothyroidism: Characterized by low T4 with low or normal TSH; may be isolated or associated with congenital hypopituitarism 4
- Subclinical hypothyroidism: High TSH with normal T4 and T3 levels; controversy exists regarding necessity of treatment 5
Pitfalls to Avoid
- Delaying treatment while awaiting imaging studies 1
- Failing to consider hypothyroidism despite normal screening results when clinical symptoms are present 2
- Missing central hypothyroidism in TSH-only screening programs 3
- Discharging mothers too early postpartum, which increases false positive TSH elevations 3
Early diagnosis and prompt treatment are essential, as treatment started within the first 2 weeks of life prevents mental retardation in >90% of children with congenital hypothyroidism 5.