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Hypothyroidism C015

Last amended 
12 November 2019
Current RMA Instruments
Reasonable Hypothesis SOP
29 of 2013
Balance of Probabilities SOP
30 of 2013
Changes from previous Instruments

SOP Bulletin 165

ICD Coding
  • ICD-9-CM Codes: 244.0-9 
  • 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 cuases of hypothyroidism is Hashimoto's thyroiditis.  This condition is covered by a separate SOP and is excluded from the hypothyroidism 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.

The appropriate specialist is an endocrinologist.

Additional diagnoses covered by SOP
  • Central hypothyroidism
  • Myxedema
  • Primary hypothyroidism
  • Secondary or tertiary hypothyroidism
Conditions excluded from SOP
  • Congenital hypothyroidism#
  • Congenital iodine deficiency syndrome#
  • Hashimoto’s thyroiditis*
  • Hyperthyroidism*
  • Sick euthyroid syndrome#
  • Subclinical hypothyroidism (N.I.F.)
  • Transient hypothyroidism during recovery form 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.