🦋 Abnormal TFTs — Assessment & Management

RCGP SCA Algorithm — UK Primary Care

RCGP SCA10-min consult
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Abnormal TFTs — Assessment & ManagementTSH interpretation · Graves' disease · Hashimoto's · carbimazole agranulocytosis · levothyroxine titration · pregnancy TFTs · subclinical thyroid · amiodarone
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⚡ Snapshot. The whole pathway on one page: act now, triage, classify, treat today and safety-net. The Steps tab holds the detail.

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1
Safety

Red Flags — Thyroid Storm, Myxoedema Coma & Malignancy

Scope: adult primary-care guide. Pregnancy (NICE NG145 excludes thyroid disease in pregnancy — see RCOG Green-top Guideline 76), children and young people, thyroid cancer and thyroid emergencies need specialist or local pathways. Refer via the local endocrinology referral or Advice & Guidance route, and follow the local formulary and shared-care arrangements.
Suppressed TSH or known/suspected thyrotoxicosis + fever + marked tachycardia or AF + any of agitation, confusion or reduced consciousness, heart failure, or vomiting, diarrhoea or jaundice Suspected thyroid storm — a clinical diagnosis and a medical emergency; do not wait for TFTs. → Call 999, arrange immediate transfer to hospital and discuss with critical care/endocrinology. Do not delay transfer to calculate a score (a Burch–Wartofsky score is not required for the diagnosis) or to give a complex drug regimen. ABCDE assessment, ECG, glucose, temperature and relevant blood tests only if this does not delay transfer. Emergency drug treatment follows the receiving hospital's protocol.
Known or suspected hypothyroidism (often missed doses) + drowsiness, confusion or coma + hypothermia; bradycardia and hypoventilation may occur Suspected myxoedema coma — a clinical diagnosis and a medical emergency; do not wait for TFTs. → Call 999, arrange immediate transfer to hospital and discuss with critical care/endocrinology. ABCDE assessment, ECG, glucose, temperature and relevant blood tests only if this does not delay transfer. Thyroid hormone and steroid treatment is specialist/critical-care management following the receiving hospital's protocol.
Unexplained thyroid lump, whatever the TSH (more concerning with cervical lymphadenopathy, hoarse voice, dysphagia, rapid growth or a hard, fixed mass) Possible thyroid malignancy. → Consider a suspected cancer pathway referral (NICE NG12, updated April 2026) (head and neck / thyroid surgery). USS thyroid (TIRADS scoring). Fine needle aspiration biopsy if USS suspicious.
New AF with suppressed TSH in elderly patient Subclinical or overt hyperthyroidism causing AF. → ECG; manage AF according to standard AF guidance, including assessment for anticoagulation and rate control. Beta-blockers and digoxin are not interchangeable — choice depends on ventricular function, blood pressure, heart failure, asthma and the degree of sympathetic drive. Treat the underlying thyrotoxicosis and obtain specialist (endocrinology/cardiology) input. New AF with haemodynamic instability (shock, syncope, chest pain or heart failure) → call 999 (NICE NG196). Cardioversion may be required for haemodynamic instability or other clinical indications; it is not prohibited solely because the patient is not yet euthyroid.
TSH suppressed + eye symptoms: proptosis, diplopia, ophthalmoplegia, corneal exposure Graves' ophthalmopathy (thyroid eye disease). → Ask about smoking and strongly advise cessation. Assess visual acuity, colour vision, diplopia, ocular motility, corneal exposure and optic-nerve symptoms. Same-day ophthalmology for reduced visual acuity, altered colour vision, corneal ulceration/exposure, severe pain, optic-disc swelling or suspected compressive optic neuropathy. Artificial tears and smoking cessation are appropriate general measures. Selenium may be considered for mild, active, recent-onset disease, particularly in selenium-deficient areas — not a blanket treatment (EUGOGO 2021). Moderate-to-severe or sight-threatening disease → specialist thyroid-eye care (IV methylprednisolone and orbital decompression are specialist, not GP, treatments).
Raised TSH in pregnancy (above the pregnancy-specific reference range) Gestational hypothyroidism. → Interpret using the local laboratory's trimester-/pregnancy-specific reference range. Treat overt hypothyroidism promptly; consider levothyroxine when TSH is above the pregnancy-specific range and below 10 mIU/L, particularly when newly diagnosed in the first trimester (RCOG Green-top Guideline 76). Discuss with the local antenatal endocrine pathway.
Suspected thyroid storm and myxoedema coma are medical emergencies managed in hospital. In primary care the priority is recognition and immediate transfer. Precipitants of thyroid storm include thyroid surgery, radioiodine therapy, iodinated contrast agents, acute illness, trauma and abrupt discontinuation of antithyroid drugs. Scoring systems such as Burch–Wartofsky are not required to diagnose thyroid storm and should not delay transfer. Beta-blockade is not universally safe (shock, heart failure, severe asthma), and antithyroid-drug, iodine and steroid dosing should follow the receiving hospital/endocrine/critical-care protocol. In pregnancy, TSH normally falls in the first trimester because of hCG cross-reactivity with TSH receptors, so results must be interpreted against the local laboratory's pregnancy-specific reference range rather than non-pregnant ranges or fixed universal thresholds.
2
Diagnose

Interpreting TFT Results — A Systematic Approach

TSH low + FT4 high = Primary hyperthyroidism
Excess thyroid hormone from the gland itself. Causes: Graves' disease (TSH receptor antibodies — most common, diffuse goitre, eye disease, pretibial myxoedema), toxic multinodular goitre (TMNG — multinodular goitre + autonomous nodules, older patients), toxic adenoma (solitary hyperfunctioning nodule), thyroiditis (subacute/De Quervain's — painful goitre + raised ESR; silent/postpartum thyroiditis — painless, transient, biopsy not needed).
TSH high + FT4 low = Primary hypothyroidism
Insufficient thyroid hormone from the gland. Causes: Hashimoto's thyroiditis (autoimmune, anti-TPO antibodies, most common in women — affects 5% of women by age 60), post-radioiodine/post-thyroidectomy, iodine deficiency (rare in UK), drugs (amiodarone, lithium, carbimazole, interferon), Riedel's thyroiditis (fibrous infiltration — rare, hard fixed goitre).
TSH low + FT4 normal = Subclinical hyperthyroidism
Suppressed TSH with normal free T4/T3. Consider: early Graves', multinodular goitre, exogenous levothyroxine excess. Risks at TSH <0.1: AF, osteoporosis, ventricular hypertrophy. Repeat testing to confirm; consider seeking specialist advice if TSH is <0.1 on 2 readings at least 3 months apart with evidence of thyroid disease or symptoms of thyrotoxicosis (NICE NG145), taking into account age, AF, osteoporosis and symptoms — do not treat all older adults automatically. If TSH 0.1–0.4, asymptomatic and untreated: TSH every 6 months (NICE NG145).
TSH high + FT4 normal = Subclinical hypothyroidism
Elevated TSH with normal FT4. Most common TFT abnormality. If TSH ≥10: confirm on two occasions about 3 months apart before considering treatment (unless overt hypothyroidism, pregnancy or another indication makes treatment more urgent). If TSH above range but below 10 on 2 occasions 3 months apart: consider a 6-month trial of levothyroxine if under 65 with symptoms (NICE NG145) — if symptoms do not improve once TSH is normal, consider stopping; positive TPO antibodies raise the risk of progression to overt hypothyroidism (roughly 4% per year) and justify closer monitoring, but antibody positivity alone does not mandate treatment. If untreated: TSH + FT4 annually if features suggest underlying thyroid disease (raised TPO antibodies, previous thyroid surgery or radioiodine); otherwise every 2–3 years, or sooner if symptoms develop.
Low FT4 + low, normal or mildly raised TSH
May indicate central hypothyroidism, but also consider: acute or non-thyroidal illness; glucocorticoids, dopamine and other drugs; assay interference; pregnancy-related reference-range issues; recent treatment changes. If central hypothyroidism is suspected, assess the other pituitary axes — particularly a 9 am cortisol before starting levothyroxine where feasible — and refer urgently to endocrinology.
High FT4 + normal or non-suppressed TSH
Not automatically central disease. Consider: assay interference (particularly biotin, or heterophile antibodies), levothyroxine taken shortly before blood sampling, thyroid hormone resistance, TSH-secreting pituitary adenoma, analytical error. Discuss with the laboratory and endocrinology.
Testing strategy (NICE NG145)
TSH alone initially in most adults, with FT4 added if TSH is abnormal; measure both TSH and FT4 initially if pituitary disease is suspected. Ask specifically about biotin — biotin-containing supplements can produce a falsely low TSH and falsely high FT4/FT3.
The subclinical hypothyroidism treatment threshold is one of the most debated areas in thyroid medicine — the evidence base for treating TSH between 5–10 mIU/L in the absence of symptoms and antibodies is limited. The TRUST trial (2017) — the largest RCT to date of levothyroxine in subclinical hypothyroidism in adults over 65 — showed no benefit on symptoms, quality of life, or any clinical outcome compared to placebo. However, the subset with TPO antibodies and the subset with TSH above 10 mIU/L were not well-represented in this trial, and multiple observational studies suggest these groups benefit from treatment. The current pragmatic approach: TSH ≥10 on two tests about 3 months apart = consider treatment (NICE NG145), taking into account age, symptoms, antibody status, goitre, pregnancy plans, previous thyroid treatment and cardiovascular risk; TSH above range but below 10 = consider a 6-month levothyroxine trial if under 65 and symptomatic (NICE NG145), with closer monitoring if TPO antibodies are positive; untreated subclinical hypothyroidism = TSH + FT4 annually if features suggest underlying thyroid disease (raised TPO antibodies, previous thyroid surgery or radioiodine), otherwise every 2–3 years, or sooner if symptoms develop. For patients already on levothyroxine with TSH in the 5–10 range, the dose should be titrated up — this is not 'subclinical hypothyroidism,' it is undertreated hypothyroidism.
3
Diagnose

Targeted History, Examination & Further Tests

History
Hypothyroid symptoms: fatigue, weight gain, cold intolerance, dry skin, hair loss, constipation, bradycardia, depression, menorrhagia, delayed relaxation reflexes, myalgia. Hyperthyroid symptoms: weight loss, heat intolerance, palpitations, tremor, diarrhoea, insomnia, amenorrhoea, eye symptoms (Graves'). Drug history: amiodarone (causes both hypo- and hyperthyroidism — complex, see below), lithium (hypothyroid), interferon, checkpoint inhibitors (pembrolizumab — immune thyroiditis), iodinated contrast. Recent viral illness (De Quervain's thyroiditis). Pregnancy/postpartum (gestational hypothyroid, postpartum thyroiditis). Family history (autoimmune thyroid disease).
Examination
Thyroid gland: size (normal vs goitre), consistency (soft = Graves'; firm/nodular = TMNG; very hard/fixed = malignancy or Riedel's), tenderness (De Quervain's thyroiditis), bruit (Graves' — hypervascular), asymmetry, nodule. Cervical lymphadenopathy. HR + rhythm (AF in hyperthyroidism). BP. Weight. Tendon reflexes (delayed = hypothyroidism; brisk = hyperthyroidism). Eye changes: exophthalmos, lid lag, lid retraction (Graves').
Further investigations
FT3 (confirm overt hyperthyroidism — T3 toxicosis: FT3 elevated, FT4 normal) · TSH receptor antibodies (TRAb) (preferred test to confirm Graves' disease — positive in 95%) · Anti-TPO antibodies (useful when TSH is raised; generally measure once only — also raised in Graves') · USS thyroid (palpable nodule, TIRADS — in thyrotoxicosis generally reserved for a palpable nodule; not routine for all goitres or thyrotoxicosis) · Biotin warning: biotin-containing supplements can cause a falsely low TSH and falsely high FT4/FT3 — ask about supplements · Thyroid isotope scan (hot vs cold nodules, differentiate Graves' from TMNG — specialist) · FNA biopsy (TIRADS 4–5 or clinically suspicious nodule — specialist)
TRAb (TSH receptor antibody) testing is the key diagnostic test for Graves' disease — it has approximately 95% sensitivity and 99% specificity for Graves' disease when measured with the newer third-generation assays. The clinical value: distinguishing Graves' disease (requires antithyroid drugs ± radioiodine/surgery) from thyroiditis (transient hyperthyroidism that resolves spontaneously — antithyroid drugs not needed) without requiring isotope scanning. In a patient with suppressed TSH + elevated FT4 + positive TRAb = Graves' disease diagnosis confirmed. If TRAb is negative in a thyrotoxic patient: consider thyroiditis (subacute De Quervain's — painful thyroid, raised ESR, often post-viral; postpartum thyroiditis — 4–12 months postpartum, no pain), TMNG (USS shows nodular gland), or toxic adenoma (USS shows single hot nodule). Amiodarone-induced thyroid dysfunction is a complex special case: amiodarone is iodine-rich and can cause both hypo- and hyperthyroidism. Amiodarone-induced thyrotoxicosis cannot be reliably classified as type 1 or type 2 in primary care — it needs endocrine/cardiology assessment, often with Doppler ultrasound and specialist interpretation. Patients on amiodarone need baseline and periodic thyroid, liver and pulmonary monitoring according to the local amiodarone shared-care protocol.
4
Diagnose

Special Populations — Pregnancy, Elderly & Amiodarone

Pregnancy and thyroid disease
NICE NG145 excludes pregnancy — follow RCOG Green-top Guideline 76 and the local antenatal endocrine pathway. Use the local laboratory's pregnancy-specific reference range whenever available. Treat overt hypothyroidism promptly; consider levothyroxine when TSH is above the pregnancy-specific range and below 10 mIU/L, particularly if newly diagnosed in the first trimester. Before conception, aim for TSH ≤2.5 mU/L in women treated for overt hypothyroidism or severe subclinical hypothyroidism; consider the same target in subclinical hypothyroidism, particularly if TPO-antibody positive. Women already on levothyroxine: empirical dose increase immediately after a positive pregnancy test (about 25–30%: double the dose on 2 days each week, or increase by 25 micrograms/day if the pre-pregnancy dose is ≤100 micrograms/day, or 50 micrograms/day if >100 micrograms/day), TFTs within 4 weeks, then TSH + FT4 every 4–6 weeks until 20 weeks and again around 28 weeks (or per local pathway); keep FT4 within the trimester-specific range and avoid overtreatment. Current or previous Graves' disease (including after radioiodine or surgery): measure TRAb — fetal/neonatal Graves' can occur despite maternal hypothyroidism. Refer all pregnant women needing antithyroid drugs to obstetric/endocrine care. Postpartum thyroiditis: affects 5–10% of women; biphasic pattern (hyperthyroid phase 1–4 months → hypothyroid phase 4–8 months → usually euthyroid by 12 months). Screen at 3 and 6 months postpartum in women with TPO antibodies or prior postpartum thyroiditis. 20–30% develop permanent hypothyroidism.
Elderly patients
Atypical hypothyroid presentation: lethargy, cognitive decline, depression, constipation — often attributed to ageing. Atypical hyperthyroid: AF without classic symptoms ("apathetic hyperthyroidism" — weight loss, fatigue, AF, no anxiety or tremor). Subclinical hyperthyroidism with TSH <0.1 on 2 readings at least 3 months apart and evidence of thyroid disease or symptoms: consider seeking specialist advice (NICE NG145), weighing AF and osteoporosis risk — treatment is not automatic in all older adults. Consider starting levothyroxine at a lower dose (25–50 mcg OD, NICE NG145) and titrate slowly (avoid precipitating angina/AF in those with IHD).
Amiodarone + TFTs
A mildly raised TSH, raised FT4 and low FT3 may occur during treatment, but interpret results with the clinical picture and prior TFTs. Baseline and periodic thyroid, liver and pulmonary monitoring according to the local amiodarone shared-care protocol. Amiodarone-induced hypothyroidism (AIH): treat with levothyroxine if symptomatic or TSH >10. Amiodarone-induced thyrotoxicosis (AIT): cannot be reliably classified as type 1 or type 2 in primary care — refer for joint endocrinology/cardiology assessment (often Doppler ultrasound and specialist interpretation). Do not stop amiodarone independently — continuation is a cardiology decision.
Pregnancy TFT interpretation requires specific laboratory ranges — the TSH reference range changes across each trimester due to hCG cross-stimulation of TSH receptors (hCG is structurally similar to TSH). Pregnancy reference ranges are laboratory- and assay-manufacturer-specific. GPs must use trimester-specific or pregnancy-specific reference ranges when interpreting TFTs in pregnant women — applying non-pregnant reference ranges will lead to over-treatment in the first trimester (where a low TSH may be normal due to hCG stimulation) and under-treatment in the third trimester. RCOG Green-top Guideline 76 (2025) recommends considering levothyroxine when TSH is above the pregnancy-specific reference range and below 10 mIU/L, particularly when newly diagnosed in the first trimester; it does not support a universal "TSH >2.5 plus TPO antibodies" rule. Women already on levothyroxine should increase the dose empirically on a positive pregnancy test and have TFTs within 4 weeks, keeping FT4 within the trimester-specific range and avoiding overtreatment.
5
Refer

Referral Pathways

999
Thyroid storm · Myxoedema coma
Endocrinology (urgent 2 weeks)
New overt hyperthyroidism (TSH <0.1 + elevated FT4) for cause identification + treatment planning — confirmed hyperthyroidism generally needs specialist involvement, particularly in pregnancy, significant cardiac disease or AF, thyroid eye disease, amiodarone-associated thyrotoxicosis, suspected toxic nodular disease, children and young people, and severe biochemical thyrotoxicosis · Thyroid eye disease (same-day ophthalmology if sight-threatening features) · Suspected thyroid malignancy (suspected cancer pathway) · Amiodarone-induced thyrotoxicosis · Suspected central hypothyroidism (low FT4 with low, normal or mildly raised TSH — 9 am cortisol before levothyroxine where feasible) · Use the local endocrinology referral or Advice & Guidance route
Endocrinology / thyroid surgery (suspected cancer pathway)
Unexplained thyroid lump, whatever the TSH → consider a suspected cancer pathway referral (NICE NG12) — more concerning if firm/hard, fixed, rapidly growing, with hoarse voice or lymphadenopathy, or TIRADS 4–5 on ultrasound
Obstetric endocrinology / high-risk antenatal
Thyroid disease in pregnancy, via the local antenatal endocrine pathway — all pregnant women needing antithyroid drugs; current or previous Graves' disease (TRAb); overt or significant hypothyroidism
GP management
Hypothyroidism: levothyroxine initiation + titration. Subclinical hypothyroidism TSH ≥10 on two tests about 3 months apart: consider treatment. Subclinical hypothyroidism TSH above range but below 10 on 2 occasions + symptoms, under 65: consider 6-month trial (NG145). Overt hyperthyroidism: refer to endocrinology and consider a beta-blocker while waiting (NICE NG145); carbimazole started by, or on the advice of, the specialist. Subclinical hyperthyroidism TSH 0.1–0.4, asymptomatic, age <65: if untreated, TSH every 6 months.
Carbimazole for overt hyperthyroidism is started by, or on the advice of, the specialist (NICE NG145: refer, and consider a beta-blocker while waiting). Where waiting times are long, seek specialist advice so that treatment starts promptly (rather than waiting weeks for an endocrinology appointment) — this reduces the risk of complications (AF, osteoporosis, cardiac failure from thyrotoxic cardiomyopathy). Carbimazole doses are specialist-directed. The GP who prescribes carbimazole on specialist advice or under shared care should: (1) check FBC and LFTs before starting; (2) check TSH, FT4 and FT3 about every 6 weeks until TSH is in range, then TSH every 3 months while treatment continues; (3) not routinely monitor FBC and LFTs in asymptomatic patients, but check them urgently if symptoms suggest agranulocytosis or hepatic dysfunction; (4) explain that carbimazole must be taken every day — missing doses allows rebound thyrotoxicosis; (5) counsel on effective contraception and the MHRA warnings (congenital malformations; acute pancreatitis). Agranulocytosis is rare but serious and occurs most commonly in the first 3 months; after agranulocytosis, do not restart any antithyroid drug without specialist advice (NICE NG145). Every patient starting carbimazole must receive written or verbal information: 'If you develop a sore throat, fever, mouth ulcers, bruising or marked malaise while taking this medication, stop it and get urgent medical advice and a blood test the same day.'
6
Treat

Hypothyroidism — Levothyroxine Initiation & Titration

Starting levothyroxine
Adults under 65 without cardiovascular disease: consider about 1.6 mcg/kg/day (commonly 50–100 mcg OD), adjusted to clinical circumstances. Aged 65 or over, or cardiovascular disease: consider starting low, 25–50 mcg OD (NICE NG145), and titrate cautiously (avoid precipitating angina or AF). Do not use a fixed dose without considering body weight, frailty, cardiac status and duration/severity of hypothyroidism. Take consistently on an empty stomach, ideally 30–60 minutes before breakfast, or at bedtime at least 3–4 hours after food. Separate calcium and iron by at least 4 hours. Consider impaired absorption with antacids, bile-acid sequestrants, orlistat, sucralfate, some PPIs, coeliac disease and other GI disorders — the key is consistent administration and monitoring, not a fixed interval for every drug. Generic prescribing is appropriate for most patients; if symptoms or biochemical control change after switching products, test thyroid function and consider prescribing a consistently tolerated product (MHRA).
Dose titration target
Aim for TSH within the laboratory reference range, individualised to age, symptoms and comorbidity; avoid TSH suppression or thyrotoxicosis (NICE NG145). TSH every 3 months until stable (2 similar results within the reference range), then yearly (NICE NG145). Adjust by 25 mcg increments. Common maintenance doses: 75–200 mcg OD. Review annually when stable.
Persistent symptoms on optimal TSH
Some patients remain symptomatic despite TSH in target range on levothyroxine alone. Options: (1) Check FT4 and investigate alternative diagnoses; do not routinely increase levothyroxine to suppress TSH. (2) Combination T4 + T3 (levothyroxine + liothyronine) — NICE NG145 and the BTA/Society for Endocrinology liothyronine consensus (2023): not routinely recommended; consider a trial in select patients with persistently poor QoL despite optimal TSH (specialist decision). (3) Check other causes of fatigue: coeliac, B12, anaemia, sleep, depression.
Levothyroxine in pregnancy
Women on existing levothyroxine: empirical dose increase immediately after a positive pregnancy test — about 25–30% (double the dose on 2 days each week, or increase by 25 micrograms/day if the pre-pregnancy dose is ≤100 micrograms/day, or 50 micrograms/day if >100 micrograms/day) — then TFTs within 4 weeks. TSH + FT4 every 4–6 weeks until 20 weeks and again around 28 weeks, or per the local antenatal endocrine pathway. Interpret against the local pregnancy-specific range; maintain FT4 within the trimester-specific reference range and avoid overtreatment. Before conception, aim for TSH ≤2.5 mU/L in women treated for overt or severe subclinical hypothyroidism; consider the same target in subclinical hypothyroidism, particularly if TPO-antibody positive (RCOG Green-top Guideline 76). Return to pre-pregnancy dose postpartum and recheck TFTs at 6 weeks.
The levothyroxine timing and absorption interaction is one of the most common causes of inadequate treatment response in hypothyroidism — levothyroxine is poorly absorbed when taken with food, calcium supplements, iron supplements, PPIs, and various other medications. The standard advice (take 30–60 minutes before breakfast on an empty stomach) achieves maximum absorption. However, patient adherence to this timing is poor in practice. The bedtime alternative (levothyroxine taken at bedtime, at least 3–4 hours after food) has been shown in multiple RCTs to achieve equivalent or marginally superior TSH control compared to morning dosing, and may improve compliance by integrating the medication into the established bedtime routine. The key interactions: calcium carbonate reduces levothyroxine absorption when co-administered — patients taking calcium supplements (for osteoporosis) should take levothyroxine and calcium at least 4 hours apart. Iron supplements similarly reduce absorption. Antacids, orlistat, some PPIs and coeliac or other GI disease may also impair absorption — the important point is consistent administration and monitoring, not a fixed separation interval for every drug. Cholestyramine, colestipol, and sucralfate severely impair absorption.
7
Treat

Hyperthyroidism — Antithyroid Drugs, Radioiodine & Surgery

Carbimazole (first-line antithyroid drug)
Doses are specialist-directed. NICE NG145 permits either titration (reduce dose as TFTs normalise) or block-and-replace (adds levothyroxine) for adults with Graves' disease; titration is often preferred to minimise antithyroid-drug exposure, and block-and-replace must not be used in pregnancy. Check FBC and LFTs before starting. TSH, FT4 and FT3 about every 6 weeks until TSH is in range, then TSH every 3 months while treatment continues. No routine FBC/LFT monitoring if asymptomatic — urgent FBC (and LFTs) if symptoms. Stop and seek urgent medical advice if sore throat, fever, mouth ulcers, bruising or marked malaise (agranulocytosis — urgent FBC); after agranulocytosis do not restart any antithyroid drug without specialist advice. MHRA: risk of acute pancreatitis; congenital malformations (especially weeks 6–10 of pregnancy and at higher doses) — women of childbearing potential should use effective contraception and seek advice urgently if pregnancy occurs. Many patients with Graves' disease receive a 12–18-month course; definitive treatment is considered for relapse, persistent disease, toxic nodular disease, adverse effects, patient preference or unsuitable circumstances.
Propylthiouracil (PTU)
Specialist-led only — PTU prescribing usually stays with specialist care until stable (local formulary). Second-line antithyroid drug; specialist-directed dose — BNF adult: initially 200–400 mg daily (in divided doses or once daily) until euthyroid, then reduced to 50–150 mg daily maintenance; lowest effective dose in pregnancy. Not preferred for routine long-term treatment. Used preconception and in early pregnancy (carbimazole has a more characteristic embryopathy risk) and in hospital treatment of thyroid storm. Rare but potentially severe hepatotoxicity — patients must report jaundice, dark urine, pale stools, pruritus, nausea or abdominal pain urgently. Any switch from PTU to carbimazole later in pregnancy is specialist-timed (may be around 20 weeks rather than automatically at the end of the first trimester).
Radioiodine (I-131)
Definitive treatment for Graves' or TMNG. Single outpatient oral dose; success depends on dose, diagnosis, thyroid size and local practice. Side effects: may worsen thyroid eye disease (steroid prophylaxis is risk-based and specialist-directed). Contraindicated in pregnancy and breastfeeding; avoid pregnancy for at least 6 months afterwards (follow the nuclear-medicine team's instructions). Unsuitable or relatively unsuitable in active thyroid eye disease, suspected malignancy or significant compression. Patient must be rendered euthyroid with carbimazole before radioiodine (avoid thyroid storm). Isolation requirements post-treatment (radiation safety).
Surgery (thyroidectomy)
Total thyroidectomy for: large goitre causing compressive symptoms, coexisting malignancy, patient preference. Complications: hypoparathyroidism (temporary or permanent — hypocalcaemia + tetany), recurrent laryngeal nerve injury (hoarseness). Post-thyroidectomy: lifelong levothyroxine; documented postoperative calcium/parathyroid plan and clear advice about hypocalcaemia symptoms (tingling, cramps, tetany). TSH monitoring 6-weekly initially, then annually.

Next steps: see Hypothyroidism · Hyperthyroidism · Thyroid disease in pregnancy · Atrial fibrillation

Thyroid eye disease needs structured assessment: ask about smoking (strongly advise cessation) and assess visual acuity, colour vision, diplopia, ocular motility, corneal exposure and optic-nerve symptoms. Reduced acuity, altered colour vision, corneal ulceration/exposure, severe pain, optic-disc swelling or suspected compressive optic neuropathy need same-day ophthalmology. Selenium may be considered for mild, active, recent-onset disease, particularly in selenium-deficient areas — it is not a blanket treatment for all thyroid eye disease (EUGOGO 2021). Radioiodine may worsen thyroid eye disease; steroid prophylaxis is risk-based and specialist-directed, not automatically required. Moderate-to-severe or sight-threatening disease is managed by specialist thyroid-eye services (IV methylprednisolone, orbital decompression), and radioiodine is usually deferred until the eye disease is stabilised.
8
Lifestyle

Lifestyle, Monitoring & Patient Education

Levothyroxine compliance education Take daily — hypothyroidism symptoms return within weeks of stopping. Set a phone alarm or use a pill box. Empty stomach, consistently: 30–60 min before breakfast OR at bedtime (at least 3–4 hours after food). Separate calcium and iron by at least 4 hours; mention new antacids, PPIs or other medicines that may affect absorption. Keep medication at consistent temperature (not in the bathroom — humidity degrades the tablets). Annual prescription review.
Exercise in thyroid disease Hypothyroidism: fatigue and muscle pain before treatment — start gently, increase as TSH normalises. Regular exercise helps with weight loss (weight gained with hypothyroidism is mostly fluid and metabolic — responds to levothyroxine, not diet restriction alone). Hyperthyroidism: avoid high-intensity exercise until euthyroid (cardiac risk from hyperthyroid AF + thyrotoxic cardiomyopathy). Beta-blocker cover during exercise if still thyrotoxic.
Diet and thyroid disease Iodine: mild UK iodine deficiency exists in some populations (young women on dairy-free diets — dairy is primary UK iodine source). Iodine supplementation in pregnancy (150 mcg/day) is recommended by BDA for women not eating dairy. Kelp supplements: avoid — extreme iodine variability. Soya: large amounts may impair levothyroxine absorption — keep diet and dosing consistent and recheck TFTs if intake changes markedly. Cruciferous vegetables: only affect thyroid function in extremely large quantities + iodine-deficient state — normal consumption safe.
Pregnancy planning with thyroid disease Women with Graves' on carbimazole: use effective contraception and plan pregnancy with the specialist — PTU is generally used preconception and in early pregnancy; any later switch to carbimazole (because of PTU hepatotoxicity) is specialist-timed, often around 20 weeks. Lowest effective dose, titrated on FT4 (usually upper half of the pregnancy-specific range — TSH may stay suppressed). No block-and-replace in pregnancy. TRAb in current or previous Graves' (including after radioiodine/surgery). Euthyroid status target before conception. Women on levothyroxine: empirical dose increase (25–30%, e.g. two extra doses a week) immediately on a positive pregnancy test, then TFTs within 4 weeks.
Osteoporosis risk in hyperthyroidism Sustained hyperthyroidism (including subclinical with TSH <0.1) causes bone loss. Assess fracture risk using standard clinical criteria and arrange DXA where indicated, rather than routinely after every episode of hyperthyroidism. Follow general bone-health and osteoporosis guidance (including weight-bearing exercise); avoid unnecessary calcium supplementation.
Graves' disease remission and relapse After 18 months of antithyroid drug therapy: 50% achieve remission (TRAb negative + euthyroid off medication). 50% relapse — retreatment or definitive therapy (radioiodine/surgery). Predict remission: TRAb negative after 12 months of treatment = good prognosis. Small goitre = good prognosis. Relapse: antithyroid drugs can be repeated once, then definitive treatment strongly recommended. Annual TFT post-remission.
Thyroid cancer surveillance Outside the scope of this GP guide — follow the specialist thyroid cancer team's surveillance protocol, including any TSH target and tumour-marker monitoring they specify.
Autoimmune thyroid disease and other autoimmune conditions Hashimoto's thyroiditis is associated with coeliac disease, type 1 diabetes, pernicious anaemia (B12 deficiency) and Addison's disease (polyglandular autoimmune syndrome type II — AITD + T1DM + Addison's). Take an autoimmune history and investigate according to symptoms and risk — universal screening for all these conditions is not required. Any symptoms of hypoadrenalism (fatigue + dizziness + pigmentation) in a hypothyroid patient on levothyroxine who is not improving → 9am cortisol urgently.
The autoimmune thyroid disease-coeliac disease association is clinically important — coeliac disease is more common in patients with Hashimoto's thyroiditis, reflecting the shared autoimmune genetic background (HLA-DQ2/DQ8). Test (anti-tTG IgA + total IgA) according to symptoms and risk — for example GI symptoms, anaemia or unexplained variable levothyroxine requirements — rather than universally. The clinical implication: undiagnosed coeliac disease in a patient with Hashimoto's thyroiditis causes variable levothyroxine absorption (due to small intestinal malabsorption) + ongoing autoimmune stimulation. Starting a gluten-free diet in a patient with both conditions can: reduce anti-TPO antibody titres, improve levothyroxine absorption stability, and in some cases improve thyroid function test results. The polyglandular autoimmune syndrome type II (Schmidt's syndrome) association with Hashimoto's is the most important safety consideration: a patient with Hashimoto's who develops increasing fatigue despite optimal levothyroxine + dizziness + hyperpigmentation should be investigated urgently for Addison's disease (9am cortisol). Treating Addison's with cortisol replacement before levothyroxine dose increases is essential to prevent precipitating adrenal crisis.
9
Safety

Follow-Up & Monitoring Schedules

Hypothyroidism on levothyroxine
TSH every 3 months until stable (2 similar results within the reference range). Once stable: annual TFT. When to recheck sooner: new cardiac symptoms, pregnancy, significant change in weight, new medications (amiodarone, rifampicin, anticonvulsants), GI disease (malabsorption). Target: TSH within the reference range, individualised; do not increase levothyroxine to suppress TSH.
Graves' disease on carbimazole
Baseline FBC + LFTs before starting. TSH, FT4 and FT3 about every 6 weeks until TSH is in range, then TSH every 3 months while on treatment. No routine FBC/LFTs if asymptomatic; urgent FBC if sore throat, fever, mouth ulcers, bruising or marked malaise (agranulocytosis) and LFTs if jaundice, dark urine, pale stools, pruritus or abdominal pain (hepatotoxicity). TRAb at 12 months (positive = higher relapse risk if stopping). After stopping: TSH (with cascading) within 8 weeks, then every 3 months for a year, then annually (NICE NG145).
Post-radioiodine
TSH, FT4 and FT3 about every 6 weeks for the first 6 months until TSH is in range (hypothyroidism often develops within 3–6 months); if TSH is in range at 6 months, TSH at 9 and 12 months; if still in range at 12 months, TSH every 6 months unless hypothyroidism develops (NICE NG145). Offer levothyroxine when hypothyroidism develops, then annual TFTs once stable on replacement.
Subclinical hypothyroidism (watchful waiting)
Confirm with a repeat TFT (and TPO antibodies once, if not done) about 3 months later. If untreated: TSH + FT4 annually if features suggest underlying thyroid disease (raised TPO antibodies, previous thyroid surgery or radioiodine); otherwise every 2–3 years, or sooner if symptoms develop. Reconsider treatment if TSH rises to ≥10 on repeat testing, symptoms develop or pregnancy is planned — weighing age, symptoms, antibody status, goitre, previous thyroid treatment and cardiovascular risk; antibody positivity alone does not mandate treatment.
Same-day / 999
Thyroid storm features (known or suspected hyperthyroidism + fever + marked tachycardia or AF + confusion, agitation or reduced consciousness, heart failure, or vomiting, diarrhoea or jaundice) → 999 — do not wait for TFTs · Sore throat, fever, mouth ulcers, bruising or marked malaise on carbimazole → stop carbimazole + urgent FBC same day; after agranulocytosis do not restart any antithyroid drug without specialist advice · Myxoedema coma (known or suspected hypothyroidism, often with missed doses + drowsiness or confusion + hypothermia) → 999 — do not wait for TFTs
Within 1 week
New AF in patient with suppressed TSH (haemodynamically unstable → 999, NICE NG196) → manage per AF guidance (anticoagulation assessment, rate control) + urgent endocrinology · Levothyroxine patient with significant worsening fatigue/bradycardia → TFT check this week · Pregnancy confirmed in hypothyroid patient → empirical levothyroxine increase immediately (25–30%, e.g. two extra doses a week) + TFT within 4 weeks + local antenatal endocrine pathway
The carbimazole-agranulocytosis education is a BNF/CHM prescribing safety requirement — every patient starting carbimazole (or propylthiouracil) must receive the following information, documented in the clinical record: 'If you develop a sore throat, mouth ulcers, fever, bruising, marked malaise or any sign of infection while taking this medication, stop taking it immediately and attend for a blood test the same day. Do not wait for a GP appointment — call the surgery and ask for an urgent FBC, or attend A&E out of hours.' This education must be repeated at each prescription renewal. GPs who prescribe carbimazole and do not document this safety education are at medico-legal risk if agranulocytosis occurs. The agranulocytosis is typically neutropenic (ANC <0.5 × 10⁹/L), develops rapidly (within weeks of a dose change in most cases), and can cause fatal sepsis from routine mouth bacteria within 48 hours of symptom onset. Stopping carbimazole immediately at the first symptom of infection and checking FBC within hours is the only safe response. After agranulocytosis, do not restart any antithyroid drug without specialist advice (NICE NG145).
Educational use only. Adult primary-care guide; pregnancy, paediatrics, thyroid cancer and emergencies follow specialist/local pathways. Based on NICE NG145 Thyroid disease: assessment and management (2019, last updated October 2023; excludes pregnancy), RCOG Green-top Guideline 76 Management of thyroid disorders in pregnancy (2025), BTA/BSPED Guidelines for Hypothyroidism 2019, European Thyroid Association Guidelines for Hyperthyroidism 2018 (international), EUGOGO 2021, NICE NG12 Suspected Cancer (updated April 2026), MHRA Drug Safety Updates (carbimazole; levothyroxine), local formulary and amiodarone shared-care protocol, BDA Iodine Pregnancy Statement, TRUST trial NEJM 2017.
References: [1] NICE NG145 — Thyroid disease: assessment and management (recommendations, scope and limitations) · [2] RCOG Green-top Guideline No. 76 — Management of thyroid disorders in pregnancy (BJOG, April 2025) · [3] MHRA — Levothyroxine: switching between products · [4] MHRA — Carbimazole: congenital malformations and contraception · [5] MHRA — Carbimazole: risk of acute pancreatitis · [6] Local formulary — endocrine system (PTU, antithyroid drugs) · [7] EUGOGO 2021 — medical management of Graves' orbitopathy · [8] Local amiodarone shared-care protocol · [9] SPS — Carbimazole monitoring · [10] BTA/Society for Endocrinology — Use of liothyronine (T3) in hypothyroidism: consensus statement (2023)