Treatment

Diagnostic workup

There are several diagnostic tests available to assess thyroid function, however, a stepwise approach is recommended for best resource utilization. Asymptomatic patients should  not be screened for hypothyroidism. If hypothyroidism is on the ED differential, initial testing can be limited to a TSH level only. If the TSH is abnormal, this should prompt free T 4 testing to distinguish between subclinical and clinical hypothyroidism.  However, if there is reason to suspect a hypothalamic or pituitary cause, a free T 4 level should be included in the initial testing as TSH cannot  rise appropriately in response to free T 4 decline and may  appear normal.

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A diagnosis of clinical hypothyroidism in turn should prompt an outpatient autoimmune work-up including TPO antibodies and thyroglobulin antibodies. TSH concentrations  can also occur in cases of primary adrenal insufficiency, prompting further workup of this etiology.

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It is important to note that free T 4 testing is recommended as the "free" form of thyroid hormone  is the active form while 98% to 99% is inactive and bound to plasma proteins including thyroxine-binding globulin. Additionally, the thyroid gland secretes 80% T 4 and 20% T 3 , making T 4 the superior marker for thyroid gland function.

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Therefore, routine testing of total T 4 , total T 3 , free T 3 , or reverse T 3 levels of ED patients is not indicated.

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In chronically ill patients or malnourished patients, this advanced testing can aid in the diagnosis of non-thyroidal illness syndrome.

If SH is suspected in the ED from an isolated, elevated TSH level, the patient should be referred to outpatient follow-up for confirmatory TSH and free T 4 testing within 1 to 3 months. If the initial TSH is greater  than or equal to 15, follow-up should occur within 1 to 2 weeks. After confirmation of persistently elevated TSH levels, the patient should be tested for TPO antibodies and can be started on low-dose levothyroxine (25–75 μg daily) based on the categories listed  in the following paragraph .

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If treatment is initiated, repeat TSH level should be obtained in 6 weeks and levothyroxine dose adjusted accordingly. Once target TSH level is reached, patients  can be monitored with annual TSH testing.

1. TSH between 4.5 and 6.9 mU/L: Patient should be referred to primary care for testing of TPO antibodies. In patients younger than 65 years, consider treatment with levothyroxine if patient demonstrates multiple symptoms of hypothyroidism, positive TPO antibodies, progressively increasing thyrotropin levels, plan for pregnancy, or goiter.
2. TSH between 7.0 and 9.9 mU/L: Initiate levothyroxine in patients less than 65 but consider treatment in older age groups to reduce risks of strokes or coronary heart disease.
3. TSH greater than 10.0 mU/L: Initiate levothyroxine in all ages to reduce progression to overt hypothyroidism.

Therapeutic considerations

Levothyroxine therapy

Key points