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Subclinical hypothyroidism is defined as the occurrence of TSH levels exceeding the ULN, with normal serum levels of free T3 and thyroxine.
Autoimmunity is the most common cause of subclinical hypothyroidism.
The incidence of subclinical hypothyroidism is estimated at 2,500 per 100,000 person-years in women, and 700 per 100,000 person-years in men.
About 2.5% of patients progress to clinically overt hypothyroidism each year, with a higher rate of progression in patients with thyroid autoantibodies and higher thyroid stimulating hormone levels. Thyroid function normalizes spontaneously in up to 40% cases.
Prognosis and risk of recurrence
Subclinical hypothyroidism in younger patients (< 65 years of age) is associated with an increased risk of coronary artery disease, HF and cerebrovascular accident.
The following summarized guidelines for the evaluation and management of subclinical hypothyroidism are prepared by our editorial team based on guidelines from the Endocrine Society (ES 2020), the British Medical Journal (BMJ 2019), and the American Thyroid Association (ATA/AACE 2012).
Anti-TPO antibodies: measure anti-TPO antibodies as part of the initial evaluation of patients with subclinical hypothyroidism.
Indications for treatment: as per BMJ 2019 guidelines, do not initiate thyroid replacement therapy in adult patients with subclinical hypothyroidism.
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