1 Previous radioiodine therapy, thyroid surgery, and external radiation therapy can also result in mild thyroid failure.
However, the most common cause of elevated TSH is autoimmune thyroid disease. 2 Antithyroid antibodies can be detected in 80% of patients with SCH, and 80% of patients with SCH have a serum TSH of less than 10 mIU/L.īefore diagnosis of SCH, other causes of an elevated TSH level, such as recovery from nonthyroidal illness, assay variability, presence of heterophile antibodies interfering with the TSH assay, and certain cases of central hypothyroidism with biologically inactive TSH and thyroid hormone resistance, should be excluded.
2 After the sixth decade of life, the prevalence in men approaches that of women, with a combined prevalence of 10%. 2, 3 The prevalence increases with age and is higher in women. Subclinical hypothyroidism or mild thyroid failure is a common problem, with a prevalence of 3% to 8% in the population without known thyroid disease. 1 The individual range for peripheral thyroid hormones is narrower than the population reference laboratory range therefore, a slight reduction within the normal range will result in elevation of serum TSH above the normal range. Thus, serum TSH measurement is the necessary test for diagnosis of mild thyroid failure when the peripheral thyroid hormone levels are within normal laboratory range. 1 Serum TSH has a log-linear relationship with circulating thyroid hormone levels (a 2-fold change in free thyroxine will produce a 100-fold change in TSH). Subclinical hypothyroidism (SCH) is defined as a serum thyroid-stimulating hormone (TSH) level above the upper limit of normal despite normal levels of serum free thyroxine. SCH = subclinical hypothyroidism TPO = thyroperoxidase TSH = thyroid-stimulating hormone
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