Approach

Although classical overt primary hypothyroidism presents with a constellation of physical symptoms and signs confirmed by an elevated thyroid-stimulating hormone (TSH), many patients have no symptoms or vague symptoms that are not specific to hypothyroidism.[1][26]

Clinical evaluation

Symptoms of hypothyroidism include lethargy, fatigue, depression, change in voice, cold intolerance, menstrual irregularity, constipation, and weight gain.[1] Physical signs include slow speech and movement; coarse, dry skin; eyelid edema; bradycardia; hypertension; and delayed tendon reflexes.[1][27][28]​ Goiter is generally uncommon. It is more common in areas of iodine deficiency.[1][9] Goiter may also be present in autoimmune (Hashimoto) thyroiditis.[15]​​

Diagnostic testing

TSH is the most sensitive and specific for diagnosing primary hypothyroidism. It should be ordered in the initial work-up if there is a clinical suspicion of hypothyroidism.[1] Do not order more tests until the results of the TSH test are available as a TSH value within the reference range excludes the majority of primary thyroid diseases.[29]​ Normal TSH range is 0.4 to 4.0 mIU/L (there may be some variation in laboratory norms). TSH levels are elevated in primary hypothyroidism, although in subclinical disease levels may only be mildly elevated.

Free thyroxine (T4) should then be obtained to quantify the degree of hypothyroidism or if suspicion of disorders other than primary hypothyroidism.[1] Normal free T4 range is 0.8 to 1.8 nanograms/dL. In cases where the TSH is only mildly elevated, the patient is not symptomatic and the serum free T4 is normal, the diagnosis is subclinical hypothyroidism.[2]

Autoantibody testing is not necessary for diagnosis, but helps distinguish autoimmune primary hypothyroidism.[1] It is recommended that pregnant women with TSH concentrations >2.5 mIU/L should be evaluated for thyroid peroxidase antibody (TPOAb) status.[30]

It is prudent to obtain TSH, complete blood count, and fasting blood glucose in patients who present with nonspecific fatigue and weight gain. One study found patients with hypothyroidism had a higher risk of anemia compared with euthyroid participants and suggested that a reduced thyroid function at baseline increased the risk of developing anemia during the study follow-up; however, the underlying mechanisms of this link is unclear.[31]

Total cholesterol and low density lipoprotein, concentrations may be elevated in hypothyroidism.[1]

Do not order thyroid ultrasound in patients with abnormal thyroid function tests unless the patient also has a large goiter or a lumpy thyroid.[32]​ Imaging for thyroid morphology does not help to identify a specific cause of hypothyroidism.[33]

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