🦋 Adult Hypothyroidism: Starting Levothyroxine

When to use

Use to decide whether to replace and how to start: overt and central hypothyroidism need replacement, subclinical disease is treated at TSH ≥ 10 or with high-risk features, and starting dose is tailored to age/cardiac status and pregnancy.

How it works

Overt/central → replace (central: assess adrenal function first, monitor FT4). Subclinical: TSH ≥ 10 → treat; TSH < 10 with pregnancy/symptoms/TPOAb/CV risk → consider. Full dose ~1.6 μg/kg/d (~1.0 if elderly/cardiac; +30–50% in pregnancy).

Key points

• In central hypothyroidism, adrenocortical insufficiency must be assessed and corrected before levothyroxine to avoid precipitating adrenal crisis, and monitoring uses FT4 rather than TSH. (original synthesis · not guideline verbatim)
• Older patients or those with ischemic heart disease start low (25–50, or 12.5 μg/d) and uptitrate slowly.
• Pregnancy requires prompt full replacement with ~30–50% higher dose and trimester-specific TSH targets.

References

• Jonklaas J, et al. Guidelines for the Treatment of Hypothyroidism. Thyroid 2014 (ATA).
• Chinese Society of Endocrinology. Guideline for the diagnosis and management of adult hypothyroidism.

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