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Book

Subclinical Hypothyroidism

Shiva Kumar Y. Gosi  1 , Jasleen Kaur  2 , Vishnu V. Garla  3
In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan.
.
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Book

Subclinical Hypothyroidism

Shiva Kumar Y. Gosi et al.
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Excerpt

Subclinical hypothyroidism characteristically presents with normal thyroxine (T4) levels and elevated thyroid stimulating hormone (TSH) levels. Minor fluctuations in T4 levels result in considerably larger changes in TSH levels. Although TSH levels exhibit wide variability across the population, intra-individual variation remains minimal, which is secondary to a unique individual setpoint within the hypothalamic-pituitary axis for each person.

Most individuals have a log-linear relationship between TSH and T4. Still, some individuals can have a nonlinear relationship explaining the normal free T4 with TSH ≥10 mIU/L, while others may have a low T4 level. Various studies have reported the incidence of subclinical hypothyroidism to be estimated at 3% to 10% and increasing to 18% to 20% in older patients, depending on the population studied. The prevalence of subclinical hypothyroidism tends to be higher in women and older adults. Observational studies have shown that subclinical hypothyroidism (with TSH ≥10 mIU/L) correlates with an increased risk of fatal and non-fatal coronary artery disease (CAD) events, congestive heart failure, and fatal stroke.

The prevalence of this disorder is bound to increase due to the increased availability of high-sensitivity thyroid function testing. Levothyroxine is the second most commonly prescribed medication in the United States. The increased recognition and treatment or trials with levothyroxine replacement therapy in patients with subclinical hypothyroidism could partly explain why. A study from the United Kingdom showed an increased trend toward treating hypothyroidism between 2005 and 2014, from 2.3% to 3.5% of the total population.

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Conflict of interest statement

Disclosure: Shiva Kumar Gosi declares no relevant financial relationships with ineligible companies.

Disclosure: Jasleen Kaur declares no relevant financial relationships with ineligible companies.

Disclosure: Vishnu Garla declares no relevant financial relationships with ineligible companies.

References

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