Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Congenital hypothyroidism and acquired thyroid disease
Paediatrics and child health · UK scope · Sources checked 27 Aug 2026 · Clinical review pending
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Severe thyrotoxicosis or thyroid storm
Hyperthermia, extreme tachycardia, heart failure, gastrointestinal upset and neurological change in a thyrotoxic child can progress to shock and multiorgan failure.
Action: Use ABCDE, call paediatric endocrine and intensive-care teams, obtain thyroid, metabolic, cardiac and infection studies and begin the local thyroid-storm sequence: antithyroid medicine, iodine only after synthesis blockade, glucocorticoid, careful beta-blockade when haemodynamically appropriate, cooling and precipitant treatment.
Overview
Act promptly on an abnormal newborn thyroid screen, recognise acquired hypo- and hyperthyroidism across childhood and use age-appropriate biochemical confirmation, replacement, antithyroid safety monitoring and growth or developmental follow-up.
Thyroid hormone is critical for brain development, growth, bone maturation and metabolism. Primary congenital hypothyroidism usually reflects thyroid dysgenesis or dyshormonogenesis and may cause few early signs because maternal hormone crosses the placenta. Without timely replacement, neurodevelopment can be permanently impaired. The UK newborn blood-spot programme detects raised TSH, and positive pathways are designed for urgent venous confirmation, specialist review and treatment.
Examine the infant for prolonged jaundice, poor feeding, sleepiness, constipation, large fontanelle, macroglossia, umbilical hernia, hypotonia, cool mottled skin or hoarse cry, but absence of these findings is expected. Ask about prematurity, illness, iodine exposure, maternal thyroid disease and medicines because they affect results. A TSH-based screen mainly identifies primary disease; central hypothyroidism can present with low free T4 and an inappropriately normal or low TSH.
Practice
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Paediatrics and child healthOriginal SBA
Acting on newborn screening
A 9-day-old baby who appears clinically well has a newborn blood-spot result requiring referral for suspected congenital hypothyroidism. What is the best next step?
Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources
Sources and review status
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
When the screen pathway confirms primary congenital hypothyroidism, start oral levothyroxine as soon as possible, aiming for treatment by two weeks of age. Severe disease is commonly started at 10 to 15 micrograms/kg once daily; the specialist adjusts within that range and follows free T4 rapidly. Crush the prescribed tablet and give in a small measured amount that the baby will finish. Do not hide it in a full bottle. Separate from iron, calcium and some soya feeds when advised because absorption changes.
Acquired hypothyroidism is commonly autoimmune Hashimoto thyroiditis. The most discriminating childhood sign is slowing linear growth, often with preserved or increased weight. Ask about energy, cold, bowel habit, skin, hair, menses, puberty, school performance and family autoimmune history. Examine height velocity, BMI, pulse, blood pressure, goitre, reflexes and pubertal stage. Very high TSH with low free T4 indicates overt primary disease; isolated mild TSH elevation requires context, repeat testing and specialist judgement rather than automatic lifelong treatment.
Hyperthyroidism in children is usually Graves disease. Sympathetic and metabolic features include tremor, tachycardia, heat intolerance, sweating, weight loss, emotional lability, poor concentration and increased stool frequency. A diffuse goitre, lid retraction or proptosis supports Graves. Obtain TSH and free T4, adding free T3 when TSH is suppressed and free T4 does not explain the clinical picture. TSH-receptor antibodies support autoimmune classification.
Carbimazole is typical initial antithyroid treatment under paediatric endocrine supervision, with dose titration or a selected block-and-replace approach. Families need written agranulocytosis and liver-injury advice before the first dose. Fever, sore throat or mouth ulceration means stop carbimazole and obtain an urgent full blood count; jaundice, dark urine or pruritus needs urgent liver assessment. Beta-blockade may control severe tremor and tachycardia temporarily but does not treat hormone production.
A thyroid nodule, hard asymmetry, cervical lymph nodes, stridor or progressive dysphagia is not routine autoimmune disease. Arrange urgent paediatric thyroid expertise and ultrasound by an experienced service; ultrasound does not decide malignancy alone, and radionuclide scanning is not a default goitre test. Thyroid storm is rare but presents with severe hyperthermia, cardiovascular dysfunction and neurological disturbance, requiring parallel resuscitation, antithyroid therapy, iodine timed after antithyroid medicine, glucocorticoid and intensive support.
Follow-up must protect growth and development as well as normalise numbers. In congenital disease, monitor free T4 and TSH frequently during infancy, after dose changes and through rapid growth, and track hearing and neurodevelopment. In acquired disease, repeat tests at appropriate intervals and ask about missed doses or interacting supplements before escalating. Adolescents taking levothyroxine deserve pregnancy counselling because dose requirements rise early in pregnancy, while Graves therapy requires planned specialist preconception review.
Key points
Most babies with congenital hypothyroidism look well at birth, so the UK newborn blood-spot programme and rapid follow-up of raised TSH are essential for preventing neurodevelopmental harm.
A screen-positive result is not the diagnosis: obtain urgent venous TSH and free T4 through the designated paediatric pathway, but do not create avoidable delay in treatment.
Start levothyroxine promptly when primary congenital hypothyroidism is confirmed, ideally within the first two weeks; severe disease usually needs 10 to 15 micrograms/kg once daily under specialist care.
Blood-spot TSH screening may not detect central hypothyroidism, so prolonged jaundice, hypoglycaemia, micropenis, midline abnormality or other pituitary signs still need serum free T4 and endocrine assessment.
Acquired primary hypothyroidism often causes slowing height velocity, fatigue, constipation, cold intolerance, dry skin, delayed puberty, goitre and deteriorating school function; weight gain alone is nonspecific.
First-line biochemical assessment for suspected primary disease is TSH, adding free T4 when TSH is abnormal; assess both together immediately when pituitary disease is possible.
Graves disease can cause weight loss despite appetite, heat intolerance, tremor, tachycardia, anxiety, diarrhoea, goitre, eye signs and accelerated growth, sometimes with impaired school concentration.
Aetiology
01
Thyroid dysgenesis
Absent, ectopic or underdeveloped thyroid tissue causes most permanent primary congenital hypothyroidism and is usually sporadic.
02
Hormone synthesis defects
Inherited dyshormonogenesis impairs iodine handling or thyroid-hormone production, often causing a gland in the normal position that may enlarge.
03
Autoimmune thyroid disease
Hashimoto thyroiditis destroys hormone-producing tissue, whereas Graves antibodies stimulate the TSH receptor and cause excess production.
04
Central or treatment-related disease
Pituitary or hypothalamic defects, surgery, irradiation, medicines and iodine exposure can produce thyroid dysfunction with non-classic TSH patterns.
Pathophysiology
1
Neurodevelopmental hormone deficiency
Insufficient thyroxine during early brain maturation disrupts neuronal migration, myelination and synaptic development, making treatment timing crucial.
2
Reduced metabolic signalling
Low thyroid hormone slows thermogenesis, gastrointestinal motility, cardiac rate, bone maturation and growth-plate activity across multiple organs.
3
Feedback-axis response
Primary gland failure lowers free T4 and raises pituitary TSH, while central disease produces low free T4 without an appropriate TSH rise.
4
Receptor stimulation
Graves immunoglobulins activate the TSH receptor continuously, increasing hormone synthesis, gland growth and adrenergic tissue sensitivity.
Clinical features and red flags
Screen-detected congenital disease
An apparently healthy newborn has raised blood-spot TSH and requires rapid venous confirmation through the screening pathway.
Symptomatic infant
Prolonged jaundice, poor feeding, constipation, macroglossia, hypotonia, large fontanelle and cool skin indicate established deficiency.
Acquired hypothyroidism
Falling height velocity with fatigue, cold intolerance, constipation, dry skin, goitre and delayed puberty is characteristic.
Central thyroid deficiency
Low free T4 without an appropriate TSH rise plus hypoglycaemia, midline or other pituitary signs suggests central disease.
Fever, marked tachycardia, heart failure, vomiting, agitation, delirium or coma in thyrotoxicosis requires emergency intensive care.
Red flags requiring action
A positive congenital hypothyroidism screen requires urgent venous confirmation and specialist action even when the baby appears well.
Prolonged neonatal jaundice with hypoglycaemia, micropenis or midline abnormality can indicate central pituitary disease missed by TSH screening.
Fever, sore throat or mouth ulcers while taking
Investigations
01Urgent venous TSH and free T4First step
Why
Confirm an abnormal newborn screen or define suspected primary and central thyroid dysfunction.
Interpretation and limitations
High TSH with low free T4 indicates primary failure; low free T4 without appropriate TSH elevation raises central disease.
02First-line childhood thyroid functionFirst line
Why
Assess symptomatic acquired disease using TSH, adding free T4 when TSH is outside range or pituitary disease is suspected.
Interpretation and limitations
Use age-specific ranges and repeat borderline results after illness; discordant values suggest assay, medicine or central-axis issues.
03Thyroid autoantibodies
Why
Support Hashimoto disease with thyroid peroxidase antibodies or Graves disease with TSH-receptor antibodies.
Interpretation and limitations
Antibodies classify the mechanism but do not replace hormone measurement or determine severity by titre alone.
04Growth and bone-age assessment
Why
Quantify chronicity and developmental effect when height velocity or puberty is altered.
Interpretation and limitations
Delayed bone age supports prolonged hypothyroidism but also occurs in constitutional delay and other endocrine disease.
Differential diagnosis
01
Normal growth variation
Familial short stature and constitutional delay preserve a coherent growth pattern without the systemic hypothyroid features or abnormal biochemistry.
02
Non-thyroidal illness
Severe acute disease can transiently lower thyroid hormones and alter TSH, so tests obtained during illness need cautious interpretation.
03
Obesity-related TSH elevation
A modest TSH rise with normal free T4 may accompany obesity and often improves with health change rather than indicating gland failure.
04
Anxiety or stimulant effect
Tremor, palpitations and weight change can reflect anxiety, medicines or substances, but suppressed TSH with raised hormones supports thyrotoxicosis.
Management
01Positive newborn screenConfirm and replace without delayFirst stepThe screening laboratory reports a congenital hypothyroidism result requiring clinical referral.+
1Contact the family through the designated pathway, assess the infant and obtain urgent venous TSH and free T4.
2Start specialist-prescribed levothyroxine promptly when confirmed, commonly 10 to 15 micrograms/kg/day for severe primary disease.
3Teach reliable administration and arrange early free-T4 and TSH checks, hearing, growth and neurodevelopmental follow-up.
02Acquired hypothyroidismConfirm severity and restore euthyroidismGrowth slowing, goitre or systemic symptoms accompany primary hypothyroid biochemistry.+
1Review illness, medicines, supplements and autoimmune features and measure antibodies where classification will help.
2
Complications
01
Permanent developmental impairment
Untreated severe congenital deficiency can cause intellectual, motor and hearing disability despite few physical signs at birth.
02
Impaired growth and puberty
Chronic hypothyroidism slows linear growth and bone age and can delay or occasionally distort pubertal development.
Excess levothyroxine harms sleep, bone and cardiovascular health, while antithyroid medicines can cause agranulocytosis, hepatitis or rash.
Monitoring and follow-up
In congenital disease, repeat free T4 and TSH soon after initiation and frequently through infancy, rapid growth and every dose change.
Plot length or height, weight, head circumference in infancy, bone maturation when relevant and pubertal progression over time.
Review how levothyroxine is prepared, whether the full dose is swallowed and timing relative to iron, calcium, soya and medicines.
For Graves disease, follow free T4 and free T3 during early treatment because TSH may remain suppressed after hormone control.
Ask at every antithyroid review whether fever, sore throat, mouth ulcers, rash, jaundice, pruritus or abdominal pain has occurred.
Assess pulse, blood pressure, goitre, eye signs, sleep, school function and psychological wellbeing alongside biochemistry.
Provide adolescent pregnancy and transition planning because both levothyroxine needs and antithyroid risk require early specialist adjustment.
Special situations
A well baby may be affected
Screening succeeds because congenital hormone deficiency often precedes recognisable clinical signs by weeks or months.
TSH screening has a blind spot
Central hypothyroidism may have no TSH rise, so pituitary clues require direct serum free-T4 assessment.
Height is more specific than weight
Acquired hypothyroidism typically slows linear growth; uncomplicated obesity more often preserves or accelerates height velocity.
Replace cortisol before thyroid
Increasing metabolism with levothyroxine can expose dangerous adrenal deficiency when central pituitary disease affects both axes.
A sore throat changes the plan
Carbimazole-related agranulocytosis is rare but serious enough that immediate cessation and blood count are mandatory.
Common pitfalls
01
Waiting for physical signs before acting on a positive newborn screening result.
02
Assuming a normal blood-spot TSH excludes central hypothyroidism.
03
Mixing levothyroxine into a full bottle that the baby may not finish.
04
Calling weight gain alone hypothyroidism without assessing height velocity and thyroid tests.
05
Starting levothyroxine before considering cortisol deficiency in suspected pituitary disease.
06
Ordering ultrasound routinely for every goitre rather than answering a structural question.
07
Continuing carbimazole through fever or sore throat without an urgent blood count.
08
Using persistent TSH suppression early in Graves treatment as the sole reason for excessive dose escalation.
A child taking carbimazole who develops fever, sore throat or mouth ulcers must stop the medicine and obtain an urgent full blood count because agranulocytosis can be life threatening.
Severe tachycardia, fever, agitation, heart failure, vomiting, diarrhoea or reduced consciousness with thyrotoxicosis suggests thyroid storm and requires emergency paediatric endocrine and intensive-care treatment.
Monitor TSH and free T4 with age-appropriate ranges, growth, development, adherence and dosing interactions; overtreatment in infancy also threatens development.
carbimazole
requires immediate cessation and urgent full blood count.
Jaundice, dark urine, abdominal pain or pruritus on antithyroid medicine requires urgent liver assessment.
Thyrotoxicosis with cardiovascular or neurological dysfunction is an intensive-care emergency rather than routine outpatient Graves disease.
A hard thyroid mass, cervical lymphadenopathy, voice change, stridor or progressive swallowing difficulty needs urgent specialist evaluation.
Severe headache or visual symptoms with central hypothyroid biochemistry may indicate a pituitary mass or apoplexy.
05Targeted thyroid ultrasound
Why
Assess a palpable nodule, asymmetry, suspicious nodes or selected congenital anatomy through an expert service.
Interpretation and limitations
Sonographic risk features guide fine-needle sampling; routine imaging is unnecessary for uncomplicated biochemical autoimmune disease.
06Pituitary hormone evaluation
Why
Assess cortisol, growth and gonadal axes when central hypothyroidism or a midline lesion is possible.
Interpretation and limitations
Cortisol deficiency must be considered before starting thyroid replacement because thyroxine can precipitate adrenal crisis.
Escalation
Begin age- and weight-appropriate levothyroxine under paediatric guidance, using slower escalation when longstanding severe disease warrants it.
3Recheck hormones after the prescribed interval and adjust for growth, adherence and absorption while tracking height and puberty.
03Graves diseaseControl hormone production safelySuppressed TSH and raised free hormones with clinical thyrotoxicosis suggests Graves disease.+
1Assess severity, pulse, blood pressure, ECG need, goitre, eyes and TSH-receptor antibodies and refer promptly to paediatric endocrinology.
2Use specialist carbimazole therapy with written agranulocytosis and liver-warning instructions and temporary beta-blockade when appropriate.
3DefinitiveMonitor blood counts only when symptoms indicate toxicity, follow thyroid hormones and discuss definitive therapy for relapse or poor control.
04Central diseaseProtect the adrenal axis firstFree T4 is low without a proportionate TSH rise or other pituitary features are present.+
1Assess cortisol urgently with other pituitary hormones, glucose, sodium, growth and visual or neurological symptoms.
2Provide glucocorticoid cover before levothyroxine when adrenal insufficiency is possible and seek endocrine advice.
3Arrange pituitary imaging and long-term multi-axis replacement according to the identified hypothalamic or pituitary cause.
Key medicines and prescribing safety3 treatments · regimens, roles and cautions+
Replaces essential thyroid hormone during the time-critical period for brain development and subsequent growth.
Levothyroxine for congenital hypothyroidism
Start promptly after confirmation, usually 10 to 15 micrograms/kg orally once daily for severe primary congenital disease, with the paediatric endocrine team selecting the exact starting dose and adjusting to free T4 and TSH.
Give the complete dose in a small measured volume, separate from iron or calcium, check administration and avoid both delayed normalisation and biochemical overtreatment.
Restores metabolic, growth and pubertal thyroid signalling in confirmed hormone deficiency.
Levothyroxine for acquired hypothyroidism
Give orally once daily using the child-specific age, weight, severity and cardiac context prescribed by paediatric endocrinology; reassess thyroid tests after initiation and each dose change before further titration.
Exclude or cover suspected cortisol deficiency first, review adherence and interacting supplements before increasing dose and use gradual escalation in longstanding severe disease when advised.
Inhibits new thyroid-hormone synthesis in Graves disease while remission or a definitive-treatment decision is pursued.
Carbimazole
Use a paediatric endocrine weight- and severity-based oral regimen, given once daily or divided for dose titration, with duration and any block-and-replace strategy explicitly documented by the specialist team.
Stop immediately for fever, sore throat or mouth ulcers and obtain urgent full blood count; investigate hepatic symptoms and avoid restarting after confirmed agranulocytosis.