🦋 Adult Hypothyroidism: Starting Levothyroxine
This tool guides starting levothyroxine in adult hypothyroidism by type (overt/subclinical/central), TSH, and cardiac/pregnancy status, including a starting strategy and weight-based dose estimate.
Clinical takeaway
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)
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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.
Decision support for licensed clinicians only; not a substitute for clinical judgement, diagnosis or local protocols.
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Hypothyroidism type | Overt hypothyroidism (TSH↑ + FT4↓) |
|---|---|
| TSH (for subclinical, mU/L) | 8 mU/L |
| Marked symptoms / positive TPOAb / planning pregnancy / dyslipidemia etc. | Present |
| Age > 50 yr or ischemic heart disease | Yes |
| Pregnancy | Yes |
| Weight (optional, for dose estimate) | 60 kg |
→DispositionRecommend LT4 replacement therapy
- Decision：Overt hypothyroidism (elevated TSH + low FT4) needs replacement, usually lifelong.
- Starting strategy：Pregnancy: start at full replacement dose and reach target promptly; replacement dose is ~30%–50% higher than non-pregnant, adjusted to trimester-specific TSH targets.
- Dose estimate：Full replacement dose ~ 134 μg/d (elderly/heart disease ~1.0 μg/kg; pregnancy +30–50%; titrate by thyroid function)
| Hypothyroidism type | Central hypothyroidism (FT4↓, TSH not high) |
|---|---|
| TSH (for subclinical, mU/L) | 8 mU/L |
| Marked symptoms / positive TPOAb / planning pregnancy / dyslipidemia etc. | Absent |
| Age > 50 yr or ischemic heart disease | No |
| Pregnancy | No |
| Weight (optional, for dose estimate) | 60 kg |
→DispositionRecommend LT4 replacement (first assess adrenocortical function)
- Decision：Central hypothyroidism needs replacement, but before starting LT4 first assess and correct any adrenocortical insufficiency to avoid precipitating crisis; monitor central hypothyroidism by FT4, not TSH.
- Starting strategy：Young, no heart disease: may start at full replacement dose (~1.6 μg/kg/d).
- Dose estimate：Full replacement dose ~ 96 μg/d (~1.6 μg/kg; pregnancy +30–50%; titrate by thyroid function)
Frequently asked questions
- What is Adult Hypothyroidism: Starting Levothyroxine?
- This tool guides starting levothyroxine in adult hypothyroidism by type (overt/subclinical/central), TSH, and cardiac/pregnancy status, including a starting strategy and weight-based dose estimate.
- How is Adult Hypothyroidism: Starting Levothyroxine calculated? What is the core formula?
- 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).
- When is Adult Hypothyroidism: Starting Levothyroxine used?
- 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.
- What are the key clinical points for Adult Hypothyroidism: Starting Levothyroxine?
- 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.
- What are the limits and cautions when using Adult Hypothyroidism: Starting Levothyroxine?
- For licensed clinicians and clinical researchers. Interpret results with history, investigations and local protocols; not a diagnosis or prescription, and not a substitute for multidisciplinary decision-making or local guidelines.
- How is Adult Hypothyroidism: Starting Levothyroxine calculated in practice? Can you show a worked example?
- Inputs: Hypothyroidism type Overt hypothyroidism (TSH↑ + FT4↓), TSH (for subclinical, mU/L) 8 mU/L, Marked symptoms / positive TPOAb / planning pregnancy / dyslipidemia etc. Present, Age > 50 yr or ischemic heart disease Yes, Pregnancy Yes, Weight (optional, for dose estimate) 60 kg → Result: Disposition Recommend LT4 replacement therapy（Decision: Overt hypothyroidism (elevated TSH + low FT4) needs replacement, usually lifelong., Starting strategy: Pregnancy: start at full replacement dose and reach target promptly; replacement dose is ~30%–50% higher than non-pregnant, adjusted to trimester-specific TSH targets., Dose estimate: Full replacement dose ~ 134 μg/d (elderly/heart disease ~1.0 μg/kg; pregnancy +30–50%; titrate by thyroid function)） Inputs: Hypothyroidism type Central hypothyroidism (FT4↓, TSH not high), TSH (for subclinical, mU/L) 8 mU/L, Marked symptoms / positive TPOAb / planning pregnancy / dyslipidemia etc. Absent, Age > 50 yr or ischemic heart disease No, Pregnancy No, Weight (optional, for dose estimate) 60 kg → Result: Disposition Recommend LT4 replacement (first assess adrenocortical function)（Decision: Central hypothyroidism needs replacement, but before starting LT4 first assess and correct any adrenocortical insufficiency to avoid precipitating crisis; monitor central hypothyroidism by FT4, not TSH., Starting strategy: Young, no heart disease: may start at full replacement dose (~1.6 μg/kg/d)., Dose estimate: Full replacement dose ~ 96 μg/d (~1.6 μg/kg; pregnancy +30–50%; titrate by thyroid function)）