A neonate born at term has a newborn screen showing low free T4 with a low (not elevated) TSH. The baby has micropenis and midline cleft palate. Before starting levothyroxine, which step is most important?

• A Repeat the thyroid function tests in two weeks
• B Start levothyroxine immediately at 10 microgram/kg/day
• C Perform radionuclide thyroid scanning to locate the gland
• D Assess other pituitary axes, especially serum cortisol, before treating ✓

Explanation

Low TSH with low free T4 indicates central hypothyroidism, and the associated midline defects suggest hypopituitarism. Replacing thyroid hormone in untreated cortisol deficiency precipitates an adrenal crisis, so cortisol must be assessed and hydrocortisone given if deficient. Immediate levothyroxine without this assessment is dangerous. Radionuclide scanning distinguishes primary causes and is irrelevant here since the gland itself is driven normally once the pituitary problem is addressed.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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