How do I monitor a patient with hyperthyroidism who is being treated with radioactive iodine therapy?

Consider measuring TSH, FT4, and FT3 levels in adults, children, and young people every 6 weeks for the first 6 months after radioactive iodine treatment until TSH is within the reference range.

Seek specialist endocrinology advice or arrange referral to endocrinology if: the FT4 level falls below the reference range, or the TSH level is raised, as a dose reduction or drug withdrawal of antithyroid medication may be needed; the FT4 level is persistently raised 6 months after treatment, as this may indicate suboptimal treatment; or the TSH level is greater than 20 mU/L for more than one month, as levothyroxine (LT4) replacement therapy may be needed, especially if the person has symptoms of hypothyroidism.

Monitor for complications of hyperthyroidism and adjust treatment accordingly, with blood tests interpreted by a specialist.

(NICE, 2023a)¹