When to refer:
- Suspect uncommon cause for hypothyroidism (ie. medications- amiodarone)
- Persistently raised TSH despite adequate treatment where reversible causes ( poor adherence, malabsorption, drug interactions) have been excluded
- Persistent symptoms despite treatment ( following consideration of alternative causes of symptoms)
- Suspect associated endocrine disease ie. Addisons
- Pregnancy- if profoundly hypothyroid.
- Suspect secondary hypothyroidism
If previously uninvestigated, unexplained palpable neck lump- REFER 2WW Head and Neck
Investigations prior to referral:
Primary care management:
Treat with levothyroxine
Review & recheck TSH levels every 3 months after initiation of LT4 &adjust dose to resolve symptoms and normalise TSH.
Once TSH stable, ( 2 similar readings 3 months apart)-check annually.
If elderly remember to start at lower dose.
DO NOT PRESCRIBE COMBINATION THERAPY (LT4 and LT3) or desiccated thyroxine or liquid thyroxine –these are not on formulary and should not be prescribed in primary care.
During pregnancy increase the patient’s normal dose by 25mcg and aim for a TSH below 2
-For most women following delivery, the LT4 dose should be reduced to pre-pregnancy levels, and a serum (TSH) level checked after 6 weeks.
-For any queries related to this use Endocrinology A&G
If TSH>10mU/L and fT4 in normal range:
If 70yrs or younger start treatment with LT4
If 70yrs+ consider watch and wait, if decide to treat with LT4, recheck TSH after 2months and adjust accordingly
If TSH 4-10mU/L and fT4 normal:
If <65yrs and symptomatic, consider trial LT4 assess response to treatmet 3-4months after TSH in reference range.
If older (esp >80yrs), watch and wait
In asymptomatic patients, observe and repeat TFTs in 6months.
Pitfalls interpreting TFTs
TFTs may produce misleading results in certain clinical situations, and clinical judgement should be used when interpreting results
- Following treatment for hyperthyroidism — recovery of previously suppressed thyroid-stimulating hormone (TSH) can be delayed.
- Following initiation of levothyroxine (LT4) therapy
- Non-adherence with LT4 therapy — additional doses in the days before blood monitoring can produce raised TSH and raised free thyroxine (FT4).
- Timing of blood tests — if LT4 therapy is taken shortly before blood sampling, a high TSH with normal or high-normal FT4 may result.
- Diurnal variation — the normal nocturnal peak in TSH may be delayed in night shift workers, those with irregular sleeping patterns, after vigorous exercise, and in mood disorders such as depression.
- Non-thyroidal illness ('sick euthyroid syndrome') – a wide range of acute or chronic non-thyroidal conditions, starvation, and trauma can lead to abnormal TFTs which are not due to true dysfunction of the hypothalamic-pituitary-thyroid (HPT) axis.
- TSH can be normal or low, then becomes high during recovery from acute illness. FT4 can be normal, low, or high. Free tri-iodothyronine (FT3) is usually low due to reduced conversion of thyroxine (T4) to tri-iodothyronine (T3).
- Adrenal insufficiency — may be associated with elevated TSH levels that reverse with glucocorticoid replacement.
- Obesity — may affect the HPT axis and serum TSH can become raised in overweight or obese people, which may falsely suggest subclinical hypothyroidism.
- Age — the upper limit of TSH reference ranges increases with age in adults. Mild TSH elevation (4.0–7.0 mU/L) may be a normal physiological adaption to ageing.
- Drugs — a wide range of drugs may interfere with TSH secretion; production, secretion and transport of thyroid hormones; or absorption of T4 from the gut.
- Biotin-containing supplements (bought over-the-counter) may interfere with hormone assays and cause increased TSH but normal or increased FT4.
- Kelp-containing supplements may contain excess iodine.
Clinical knowledge summary-NICE : Hypothyroidism, May 2021
The British Thyroid Foundation leaflets Your guide to hypothyroidism and Your guide to thyroid function tests.
The NHS information leaflet Underactive thyroid (hypothyroidism).
The patient information leaflet Underactive thyroid gland. Hypothyroidism available on the www.patient.info website.
- The British Thyroid Foundation leaflet Your guide to pregnancy and fertility in thyroid disorders.
Dr Duncan Browne, Consultant Endocrinologist, RCHT
Dr Bridgitte Wesson, GP and Kernow RMS Endocrinology Guideline Lead
Guidelines review 13/09/21
Next review Due 13/09/22
Dr B Wesson ( RMS GP Endocrinology lead)