Normal HS TSH Blood Test Levels
Released by the anterior pituitary gland, Thyroid stimulating hormone (TSH) works as the primary regulator of thyroid function. Accurate TSH measurement proves critically important in the diagnosis of diseases of the thyroid.
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History of TSH Test
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TSH testing in the laboratory traditionally occurs using immunoassay methodology. However, until the development of high sensitivity TSH assay methods beginning in the late 1980's, reports of normal values only provided readings of "less than 5 mIU/L."
Normal Ranges for HS-TSH Testing
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Normal ranges for the HS-TSH vary slightly according to the laboratory, methodology and instrumentation used. The normal HS-TSH reference range used by the Mayo Clinic is 0.3 to 5.0 mIU/L., with other laboratories reporting within -- or close to -- the same range.
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Hyperthyroidism: Low HS-TSH levels
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Hyperthyroidism is a condition caused by overproduction of thyroid hormones, and characterized by weight loss, fatigue, nervousness, rapid pulse and tremor. An HS-TSH level of less than 0.3 mIU/L suggests hyperthyroidism, although a confirmation of diagnosis can only occur after additional testing.
Hypothyroidism: High HS-TSH Levels
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Hypothyroidism is a condition caused by a deficiency in thyroid hormone secretion and action. It is characterized by weight gain, lethargy, depression and dry, patchy skin. An HS-TSH level greater than 5.0 mIU/L would indicate possible hypothyroidism. Additional tests often prove necessary to confirm this diagnosis.
Significance
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The ability to accurately measure TSH values less than 5 mIU/L allows the physician to distinguish between true hyperthyroidism -- which occurs at less than 0.3 mIU/L and requires treatment -- and normal patients who fall into the range between 0.3 to 5.0 mIU/L.
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References
- "Tietz Fundamentals of Clinical Chemistry;" Saunders; Sixth Edition; 2008
- National Center for Biotechnology Information: Abbreviated Tests of Endocrine Function Serum Thyroid Stimulating Hormone, Thyrotropin Releasing Hormone Test
- Mayo Clinic: Thyroid-Stimulating Hormone-Sensitive
