A newborn screening TSH cutoff is set at 20 mIU/L. A term neonate screened at 48 hours has TSH 25 mIU/L and a normal free T4. Thyroid ultrasound shows a normally located, normally sized thyroid gland. What is the most likely diagnosis?

• A Thyroid dysgenesis (ectopic thyroid)
• B TSH receptor blocking antibodies
• C Transient hyperthyrotropinemia ✓
• D Central hypothyroidism

Explanation

Mildly elevated TSH with a normal free T4 and a normally located, normally sized thyroid gland on ultrasound is most consistent with transient hyperthyrotropinemia, commonly seen after early screening (first 48 hours) due to the postnatal TSH surge or maternal factors. Dysgenesis (ectopy or aplasia) would be seen on ultrasound as an absent or misplaced gland. TSH receptor blocking antibodies cause athyreosis-like picture but ultrasound would show no gland. Central hypothyroidism shows low, not elevated, TSH.

Reference: Nelson Textbook of Pediatrics, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.