Thyroid Disorders in General Practice: Hypothyroidism, Hyperthyroidism & Nodules
From TSH interpretation to levothyroxine dosing, Graves disease management, and thyroid nodule referral
Thyroid disorders are among the most common endocrine conditions in primary care. This guide covers TSH interpretation, hypothyroidism management with levothyroxine, hyperthyroidism (Graves disease, toxic nodule), subclinical thyroid disease, and thyroid nodule assessment.
Clinical Decision Support: This article is for educational purposes and supports — not replaces — clinical judgment. Always verify with current national guidelines, BNF, and specialist consultation when needed.
Thyroid disorders are among the most prevalent endocrine conditions encountered in general practice. Hypothyroidism affects approximately 2% of the UK population (with subclinical hypothyroidism affecting a further 5–10%), while hyperthyroidism affects approximately 0.5–2%. Thyroid function tests (TFTs) are one of the most commonly requested investigations in primary care, and their interpretation requires a systematic approach.
TSH Interpretation: The First-Line Test
| TSH | Free T4 | Free T3 | Interpretation |
|---|---|---|---|
| Normal (0.4–4.0 mU/L) | Normal | Normal | Euthyroid |
| High (>4.0 mU/L) | Low | Low | Primary hypothyroidism |
| High (>4.0 mU/L) | Normal | Normal | Subclinical hypothyroidism |
| Low (<0.4 mU/L) | High | High | Primary hyperthyroidism |
| Low (<0.4 mU/L) | Normal | Normal | Subclinical hyperthyroidism |
| Low (<0.4 mU/L) | Low/Normal | Low/Normal | Secondary hypothyroidism (pituitary/hypothalamic) |
TSH is the most sensitive test for thyroid dysfunction. A normal TSH virtually excludes primary thyroid disease. Free T4 and T3 should only be checked if TSH is abnormal, or if secondary hypothyroidism is suspected (pituitary disease).
Hypothyroidism: Levothyroxine Prescribing
When to Start Treatment
- Overt hypothyroidism (high TSH + low T4): Always treat
- Subclinical hypothyroidism (high TSH + normal T4): Treat if TSH >10 mU/L, or if TSH 4–10 mU/L with symptoms, positive TPO antibodies, or pregnancy
- Do not treat subclinical hypothyroidism with TSH <10 mU/L in asymptomatic patients — risk of over-treatment (AF, osteoporosis)
Levothyroxine Dosing
- Starting dose: 50–100 mcg OD (25 mcg OD in elderly, cardiac disease, or severe hypothyroidism)
- Titrate by 25–50 mcg every 6–8 weeks based on TSH
- Target TSH: 0.5–2.5 mU/L (lower end of normal range)
- Full replacement dose: approximately 1.6 mcg/kg/day
- Take on empty stomach, 30–60 minutes before food; separate from calcium, iron, PPIs by 4 hours
- Check TSH 6–8 weeks after each dose change; annually once stable
Hyperthyroidism: Causes and Management
Common Causes
- Graves disease (70–80%): Autoimmune; diffuse goitre; ophthalmopathy; pretibial myxoedema
- Toxic multinodular goitre (15–20%): Older patients; irregular goitre; no eye signs
- Toxic adenoma (5%): Single hot nodule on isotope scan
- Thyroiditis (subacute, postpartum): Transient hyperthyroidism; tender thyroid (subacute); postpartum onset
Initial Management in Primary Care
- Refer to endocrinology for all new hyperthyroidism
- While awaiting referral: Propranolol 40 mg TDS for symptom control (tremor, palpitations, anxiety)
- Do not start carbimazole without specialist guidance (risk of agranulocytosis)
- Urgent referral if: thyroid storm, severe ophthalmopathy, AF, or pregnancy
Thyroid Nodules: When to Refer
- Any thyroid nodule with: rapid growth, hoarseness, dysphagia, cervical lymphadenopathy — urgent 2-week wait referral
- Solitary nodule >1 cm: Refer for USS and FNA
- Incidental nodule on CT/MRI: Follow BTA/RCR guidelines — refer if >1 cm or suspicious features
- Multinodular goitre: Refer if compressive symptoms, retrosternal extension, or suspicious features
- Thyroid nodule in pregnancy: Refer urgently — FNA safe in pregnancy
Key Clinical Takeaways
- TSH is the first-line test — normal TSH virtually excludes primary thyroid disease
- Treat subclinical hypothyroidism only if TSH >10 mU/L, or if symptomatic/TPO positive
- Levothyroxine: start 50 mcg OD; titrate to TSH 0.5–2.5 mU/L; take on empty stomach
- All new hyperthyroidism: refer to endocrinology; use propranolol for symptom control while waiting
- Thyroid nodule with hoarseness, rapid growth, or lymphadenopathy: urgent 2-week wait referral
- Check TSH 6–8 weeks after levothyroxine dose change; annually once stable