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Thyroid assay interference — SCE Endocrinology MCQ

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HardThyroidThyroid assay interferenceSCE Endocrinology

A 64-year-old man has TSH 2.1 mU/L with free T4 34 pmol/L during acute hospital admission. He is clinically not thyrotoxic and takes heparin infusion. What is the most appropriate next step?

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

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Correct answer: ARepeat thyroid tests when clinically stable and review assay interference

Discordant thyroid tests in an unwell patient should prompt repeat testing and consideration of assay artefact, including heparin-related free fatty acid effects. Treating as Graves' disease without suppressed TSH or clinical support is inappropriate. The pearl is that thyroid tests should be interpreted with the clinical context.

Reference: Association for Clinical Biochemistry Guidance; NICE NG145