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Levothyroxine malabsorption from iron — SCE Endocrinology MCQ

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ModerateThyroidLevothyroxine malabsorption from ironSCE Endocrinology

A 39-year-old woman takes levothyroxine 125 micrograms daily after radioiodine. TSH has risen to 18 mU/L with free T4 10 pmol/L, although she reports adherence. She recently started ferrous sulfate after heavy periods and takes both tablets with breakfast. What is the most appropriate management?

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Correct answer: D — Separate levothyroxine from iron and recheck thyroid function

Iron impairs levothyroxine absorption, so administration timing should be corrected before escalating dose. Pituitary disease would not explain high TSH with low free T4 in this context. The pearl is that apparent treatment failure is often an absorption or adherence problem.

Reference: NICE NG145, BNF