Subclinical Hyper and Hypo Thyroidism - When to Treat

Subclinical hypothyroidism is defined as an increased serum TSH in the presence of a normal serum FT4 concentration. Increased refers to values above and normal to values within population-based reference ranges of these hormones. It is however not so simple to diagnose accurately subclinical hypothyroidism in day-to-day practice applying this biochemical definition. Diagnosis of subclinical hypothyroidism is hampered by uncertainty about what constitutes appropriate reference intervals, and by biologic variation in especially TSH. The upper limit of the TSH reference interval was 4.12 mU/L in the National Health and Nutrition Eamination Survey III (NHANES III) for a large reference population that was free of thyroid disease and representative of the U.S. population, in which subjects were excluded who had thyroid antibodies or were taking thyroid medications or other medications affecting thyroid measurements.