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Hypothyroidism C015

Last amended 
17 January 2022
Current RMA Instruments
Reasonable Hypothesis SOP
3 of 2022
Balance of Probabilities SOP
4 of 2022
Changes from previous Instruments

SOP Bulletin 228

ICD Coding
  • ICD-10-AM Codes: E03, E89.00
Brief description

In this condition there is a decreased level of thyroid hormone in the blood, resulting in symptoms or signs (of hypothyroidism).  If the decrease in thyroid hormone is due to a thyroid problem it is called primary hypothyroidism, and if it is due to insufficient stimulation of the thyroid gland caused by disease of the pituitary gland or hypothalamus it is called central (secondary or tertiary) hypothyroidism.  One of the common causes of hypothyroidism is Hashimoto thyroiditis.  That condition is covered by a separate SOP and is excluded from the hypothyroidism SOP.  Hypothyroidism as a manifestation of Graves disease is covered by the Graves disease SOP.

Confirming the diagnosis 

The diagnosis is based on laboratory (blood) testing. In primary hypothyroidism there is a high serum TSH and a low serum free T4 concentration.  In secondary hypothyroidism there is a low serum free T4 concentration and a serum TSH concentration that is not appropriately elevated.  There also needs to be associated symptoms or signs for the diagnosis to be confirmed.

Whether the goitre SOP, or the SOP for hypothyroidism, should be applied in cases where both an enlarged thyroid and decreased thyroid hormone function are present (and not due to one of the excluded conditions), will be a matter for judgement and medical advice.  Generally in such cases both the goitre and the decreased thyroid hormone will have a single cause (or the goitre will be a consequence of the hypothyroidism) and a single diagnostic label and determination will be appropriate.  The factors in the SOPs are nearly identical across the two SOPs so the choice of SOP will very rarely affect the outcome, but if it does, then the most beneficial SOP that is applicable should be used.  

The appropriate specialist is an endocrinologist.

Additional diagnoses covered by SOP
  • Central hypothyroidism
  • Hypothyroidism with goitre (also covered by the goitre SOP)
  • Myxoedema coma if not due to an excluded condition (e.g. Hashimoto thyroiditis)
  • Peripheral hypothyroidism 
  • Primary hypothyroidism
  • Secondary or tertiary hypothyroidism
Conditions excluded from SOP
  • Congenital hypothyroidism#
  • Congenital iodine deficiency syndrome#
  • Hashimoto thyroiditis*
  • Hyperthyroidism*
  • Sick euthyroid syndrome#
  • Subclinical hypothyroidism (N.I.F.)
  • Transient hypothyroidism during recovery from non-thyroidal illness (N.I.F.)

* another SOP applies 

# non-SOP condition

Clinical onset

The clinical features are highly variable, depending on age and the severity of the hormone deficiency.  Symptoms can include fatigue, cold intolerance, weight gain, constipation, dry skin and myalgia.  Signs can include a goitre, a slow pulse rate, coarse hair and skin, and hoarseness. Onset can be gradual or sudden (e.g. after thyroidectomy). 

Clinical worsening

Hypothyroidism tends to be a permanent condition requiring lifelong treatment with thyroid replacement therapy (thyroxine).  Worsening may be evidenced in an untreated person by a increase in symptoms or signs of hypothyroidism, or in a treated person by a need for an increased dose of medication.