Subclinical Hypothyroidism Balancing Act: Knowing When to Treat

Tyler C. Drake, MD


October 03, 2019

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When should we treat subclinical hypothyroidism? Once levothyroxine is started, it often becomes a lifelong medication that requires lifelong monitoring. Clinicians often use a thyroid-stimulating hormone (TSH) level cutoff of 10 mU/L, but one recent set of clinical practice guidelines from Europe recommend against treatment in adults with a TSH level < 20 mU/L except in women trying to become pregnant or in patients aged 30 years and younger.[1]

The American Thyroid Association and American Association of Clinical Endocrinologists maintain the view that while most nonpregnant patients with subclinical hypothyroidism with TSH levels >10 mU/L should be treatedhealth benefits for those with TSH levels ranging from 4.5 to 10 mU/L are less clear.

I recommend considering the possibility of subclinical hypothyroidism progressing to overt hypothyroidism and thinking of the underlying pathologic conditions causing the abnormal laboratory values to decide if the hypothyroidism is a permanent or temporary condition.

Permanent pathologic causes of hypothyroidism include autoimmune thyroid disease (ie, Hashimoto disease), postsurgical hypothyroidism, and postablative hypothyroidism. In the setting of subclinical hypothyroidism, it will almost exclusively be due to autoimmune thyroid disease.

Temporary causes include pathologic conditions such as recovering subacute thyroiditis, euthyroid sick syndrome, and medication-induced hypothyroidism (eg, amiodarone and lithium), as well as nonpathologic conditions such as normal physiologic changes with aging and TSH assay interference.

Do you know how to balance the potential benefits of treatment against the harms and costs of initiating a lifelong therapy? Check your knowledge with these three cases.

Case #1: An Elderly Man at a Routine Examination

A 70-year-old man comes to a primary care clinic for a routine health examination. He has a history of hypertension and type 2 diabetes, and he is taking metformin, atorvastatin, and lisinopril. He reports some mild fatigue and feeling cold in the winter but denies constipation. He has no family history of autoimmune diseases. His blood work reveals an elevated TSH level of 7.2 mU/L (normal range, 0.4-4.5 mU/L) and a normal free T4 result. Two years ago, his TSH level was 6.5 mU/L.


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