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Subclinical Hypothyroidism Management — MRCPsych Paper B MCQ

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ModerateMood DisordersSubclinical Hypothyroidism ManagementMRCPsych Paper B

A 42-year-old woman with bipolar I disorder is stable on long-term lithium. Routine 6-monthly thyroid testing shows a TSH of 5.8 mIU/L and a free T4 within the reference range. She has no symptoms of hypothyroidism and no history of thyroid surgery or radioactive iodine treatment. What is the most appropriate next step?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — Repeat TSH and free T4 in 3 months without starting levothyroxine.

Explanation lettering: C = shown as A · A = shown as C

This is asymptomatic subclinical hypothyroidism: TSH is mildly elevated but free T4 is normal. NICE recommends confirming persistence before treatment. Levothyroxine should be considered if TSH is at least 10 mIU/L on 2 occasions 3 months apart. In adults under 65 with persistent TSH elevation below 10 mIU/L, a 6-month treatment trial may be considered only when hypothyroid symptoms are present. Therefore, repeating TSH and free T4 after 3 months is appropriate. Immediate treatment (A) is not indicated after one mild elevation, while waiting for low free T4 (D) would miss treatment indications within subclinical disease. Routine monitoring without an earlier repeat (C) does not establish persistence promptly. Lithium need not be stopped (E); clinically significant lithium-associated hypothyroidism can usually be treated concurrently with levothyroxine.

Reference: National Institute for Health and Care Excellence. Thyroid disease: assessment and management (NG145), sections 1.5.1–1.5.7, 2019, updated 2023 and reviewed 2025. https://www.nice.org.uk/guidance/ng145/chapter/recommendations