Synopsis
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.
- 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.
- 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.
Key red flags
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 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.
Fever, marked tachycardia, heart failure, vomiting, agitation, delirium or coma in thyrotoxicosis requires emergency intensive care.
Investigation priorities
Confirm an abnormal newborn screen or define suspected primary and central thyroid dysfunction.
Assess symptomatic acquired disease using TSH, adding free T4 when TSH is outside range or pituitary disease is suspected.
Management branches
The screening laboratory reports a congenital hypothyroidism result requiring clinical referral.
- Contact the family through the designated pathway, assess the infant and obtain urgent venous TSH and free T4.
- Start specialist-prescribed levothyroxine promptly when confirmed, commonly 10 to 15 micrograms/kg/day for severe primary disease.
- Teach reliable administration and arrange early free-T4 and TSH checks, hearing, growth and neurodevelopmental follow-up.