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Subclinical hypothyroidism associated with increased risk of CHD

Clinical Question:
Are adults with subclinical hypothyroidism at an increased risk of coronary heart disease and mortality?

Bottom Line:
Subclinical hypothyroidism is significantly associated with an increased risk of coronary heart disease (CHD) and CHD-related mortality only in adults with a thyroid-stimulating hormone (TSH) level of 10 mIU/L to 19.9 mIU/L. Total mortality rates are not increased by subclinical hypothyroidism, regardless of TSH level. A previously published systematic review (Surks MI, et al. JAMA 2004;291:228-38) found no evidence of benefit from screening for, or treatment of, subclinical thyroid disease. (LOE = 1a)

Reference:
Rodondi N, den Elzen WP, Bauer DC, et al, for the Thyroid Studies Collaboration. Subclinical hypothyroidism and the risk of coronary heart disease and mortality. JAMA 2010;304(12):1365-1374.  [PMID:20858880]

Study Design:
Systematic review

Funding:
Government

Setting:
Various (meta-analysis)

Synopsis:
To clarify the cardiovascular risk of subclinical hypothyroidism these investigators searched MEDLINE and EMBASE for prospective cohort studies of adults who had a baseline thyroid function measurement and were then followed up for subsequent CHD morbidity and mortality. No language restrictions were applied. Two individuals independently assessed studies for inclusion and methodologic quality using standard criteria. Disagreements were resolved by discussion with a third reviewer. Subclinical hypothyroidism was defined as a serum TSH level of 4.5 mIU/L or greater to less than 20 mIU/L, with a normal T4 concentration. Analyses were adjusted for age, sex, and traditional cardiovascular risk factors. Twelve studies met eligibility criteria and 11 international prospective cohorts provided additional data. From a total of 55,287 adults, 3450 (6.2%) met the laboratory criteria for subclinical hypothyroidism. All studies had a 5% or less loss to follow-up (from 2.5 years to 20 years). Overall, there was no significant difference in CHD events, CHD mortality, and total mortality between the patients with subclinical hypothyroidism and those with euthyroidism. The risk of CHD events and CHD mortality was, however, significantly increased in the subgroup of participants with a TSH level of 10 mIU/L to 19.9 mIU/L. Total mortality was not increased with subclinical hypothyroidism, regardless of TSH level.

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