Investigating suspected thyroid dysfunction or thyroid enlargement

NICE GUIDANCE:

Indications for tests for thyroid dysfunction

Consider tests for thyroid dysfunction for adults, children and young people if there is a clinical suspicion of thyroid disease, but bear in mind that 1 symptom alone may not be indicative of thyroid disease.

Offer tests for thyroid dysfunction to adults, children and young people with:

type 1 diabetes or other autoimmune diseases, or
new-onset atrial fibrillation.

Consider tests for thyroid dysfunction for adults, children and young people with depression or unexplained anxiety.

Consider tests for thyroid dysfunction for children and young people with abnormal growth, or unexplained change in behavior or school performance.

Caution

Be aware that in menopausal women symptoms of thyroid dysfunction may be mistaken for menopause.

Do not test for thyroid dysfunction during an acute illness unless you suspect the acute illness is due to thyroid dysfunction, because the acute illness may affect the test results.

Do not offer testing for thyroid dysfunction solely because an adult, child or young person has type 2 diabetes.

Tests when thyroid dysfunction is suspected

Consider measuring thyroid-stimulating hormone (TSH) alone for adults when secondary thyroid dysfunction (pituitary disease) is not suspected. Then:

if the TSH is above the reference range, measure free thyroxine (FT4) in the same sample
if the TSH is below the reference range, measure FT4 and free tri-iodothyronine (FT3) in the same sample.

Consider measuring both TSH and FT4 for:

adults when secondary thyroid dysfunction (pituitary disease) is suspected
children and young people.

If the TSH is below the reference range, measure FT3 in the same sample.

Consider repeating the tests for thyroid dysfunction in recommendations if symptoms worsen or new symptoms develop (but no sooner than 6 weeks from the most recent test).

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Follow-up and monitoring of primary hypothyroidism

Tests for follow-up and monitoring of primary hypothyroidism

Aim to maintain TSH levels within the reference range when treating primary hypothyroidism with levothyroxine. If symptoms persist, consider adjusting the dose of levothyroxine further to achieve optimal well-being, but avoid using doses that cause TSH suppression or thyrotoxicosis.

Be aware that the TSH level can take up to 6 months to return to the reference range for people who had a very high TSH level before starting treatment with levothyroxine or a prolonged period of untreated hypothyroidism. Take this into account when adjusting the dose of levothyroxine.

Adults

For adults who are taking levothyroxine for primary hypothyroidism,

Consider measuring TSH every 3 months until the level has stabilized (2 similar measurements within the reference range 3 months apart), and then once a year.

Consider measuring FT4 as well as TSH for adults who continue to have symptoms of hypothyroidism after starting levothyroxine.

Children and young people aged 2 years and over

For children aged 2 years and over and young people taking levothyroxine for primary hypothyroidism, consider measuring FT4 and TSH:

every 6 to 12 weeks until the TSH level has stabilized (2 similar measurements within the reference range 3 months apart), then
every 4 to 6 months until after puberty, then
once a year.

Children under 2 years

For children aged between 28 days and 2 years who are taking levothyroxine for primary hypothyroidism, consider measuring FT4 and TSH:

every 4 to 8 weeks until the TSH level has stabilized (2 similar measurements within the reference range 2 months apart), then
every 2 to 3 months during the first year of life, and
every 3 to 4 months during the second year of life.